The Malicious, the Mighty, and the Mistaken
While the deliberate, selective memory deletions presented in fiction are not presently possible in actual reality, the memory-manipulation attempted in stories is often justified via the same sorts of reasons that people in real life would want to be able to perform such acts.
For example, when people lie to others about having done (or not having done) something, that deception can be seen as the expression of a wish to make the other person actually believe in an alternate reality as opposed to what actually happened. Couple the ability to lie with the ability to intimidate, and you have a recipe for exactly the sorts of things you see in common bullying. One of the most well-known manifestations of bullying behavior is that in which a bully (or group of bullies) does something unpleasant to their chosen victim, and then proceeds to tell that victim that the unpleasant thing is not happening (or that it did not happen, or that the victim was mistaken).
It cannot be denied that control over a person's memories -- if achieved -- is a form of power over that person, and many bullies have managed to gain and keep their power through convincing their victims to doubt and constantly second-guess their own recollection of events. In the absence of the capacity to literally erase memories, the bully does the next best thing: creates so much fear and doubt in his or her victim that the victim remains under the bully's control. It seems that if true memory-erasure technology did exist, then bullies would be making a beeline for it.
A variant of this "power and control" form of literal memory modification can be seen in the 1998 film Dark City. The film's "strangers" -- aliens studying humans by periodically extracting and then "loading" memories and identities into said humans so that they're never the same person for very long at all -- might be interpreted as being merely curious, but their methods are ruthless and anything but respectful. And when one character manages to avoid being re-implanted with the identity du jour intended for him by the aliens, their reaction is not one of compassion and understanding. By escaping the aliens' manipulation, the protagonist effectively diminishes some of the power held by the aliens -- and their fear of his escape demonstrates that not only had they been guarding their power carefully, they were not particularly interested in sharing it.
All that said, as strange as this may sound, non-consensual memory erasure seems to be more commonly the province of characters who are either presented as being on the side of "good" or who believe their actions to be morally and ethically justifiable (as opposed to "true evil" characters who see no need to justify their actions at all).
Sometimes, memory modification is thought to be essential to maintaining social order -- in the Harry Potter series of novels by J. K. Rowling, the denizens of the "wizarding world" consider it their duty to keep the "muggles" (that is, us mere humans) ignorant of the existence of magic. No consideration is given to the possibility of side effects, or to the imbalance of power that exists between the muggle and wizarding worlds as a result of only half the equation knowing of the existence of the other. Direct magical abuse of muggles is considered a moral atrocity, however, memory manipulation is considered not only a necessity but a kindness.
An example of coercive memory modification (as opposed to the type described in the prior example, in which the modified individuals had no awareness regarding the decision to modify them) is seen in an episode of Star Trek: The Next Generation entitled Clues, the Enterprise crew is forced to deal with a race of xenophobic aliens who are adamantly opposed to having any other beings know of their presence in the universe. The aliens are only convinced not to destroy the Enterprise when the crew agrees to have their memories wiped. The xenophobic aliens are not motivated by malice in this case, but by fear -- they truly believe that their world would be in serious danger were "outsiders" to learn of their presence. Nevertheless, the fact that memory modification is offered only as an alternative to certain destruction puts the aliens' actions squarely in the category of coercive (as opposed to consensual).
And in other cases, human (non-magical, non-"enhanced") characters might be used by immortals, wizards, powerful aliens, or even modified humans in the context of those humans having full knowledge of the proper range of strangeness and complexity in reality, but only temporarily -- once the Final Battle is fought, the humans are made ignorant of all that has transpired.
This was the case in a particular series I enjoyed tremendously as a child, and I actually ended up taking a pair of scissors to the book and cutting out the ending because it made me so upset! While I am now quite cognizant of the dramatic irony of that action on my part, the reason I was so upset in the first place was because I felt betrayed by the "good guys". I'd come to trust them throughout reading the series, but when they performed the mass memory wipe at the end, I couldn't help but feel that the "unenhanced" humans had been used as tools and not properly respected. By robbing them of the memories of their role in saving the world from evil, the magic-users showed that they saw the humans as mere pawns, rather than as real beings with a right to the understanding of reality they'd obtained through their trials in prior books.
In all the above examples of "good", neutral, or nonmalicious persons engaging in memory modification, it could be argued that the modifiers are employing Utilitarian arguments -- that is, memory manipulation is thought to be the means to an end resulting in "the greatest good for the greatest number". Utilitarians might argue that people have a right to be happy (meaning that non-consensual memory modification could be justifiable in cases where the alternative is suffering), but this sort of reasoning is part of why I am not a utilitarian myself. For one person (or group) to assert that they have the right (or perhaps even the obligation) to modify the minds of others in accordance with what they believe to be a maximized potential for happiness is to engage in rather egregious assumption-making.
First of all, when power imbalances exist between persons or groups, those with greater power should be wary of attempting to define "good" without engaging those with lesser power in the discussion. One person's idea of "good" might be very unlike another person's -- one need only read through the movie review listings in a few different newspapers to get a sense of this. Second of all, while the general desire to diminish unnecessary suffering is difficult to argue against, not everything that can look like suffering acually is suffering.
This is not to say that there are no experiences that can generally be assumed to consist mainly of either suffering or delight -- certainly, there are boundary conditions here. But there are also plenty of gray areas, and these are fraught with pitfalls and traps. What if it were possible, for instance, to make people everywhere unaware of mortality? People would go through their lives completely devoid of the potential for existential despair. There would be no impetus to research life extension since nobody would have any concept in the first place that they might die. If it turned out to be easier to erase the human concept of mortality from all minds than to actually develop life extension medicine, would it be ethical to apply this erasure?
As farfetched and unlikely as that scenario is, it is certainly worth considering from the hypothetical standpoint, since it seems that a devoted Utilitarian would be hard-pressed to come up with an argument against the application of widespread "mortality amnesia" (if it could be reasonably demonstrated that people lacking mortality awareness were less anxious, less prone to existential angst, and more likely to contribute economically). I don't know if there is a name for the philosophy I tend to hold in this regard, but regardless of how it might be labeled, it definitely involves a clause that states that truth is always better than patronizing deception -- even if knowing the truth means more anxiety and less pleasure. In attempting to develop a comprehensive, appropriately flexible neuroethics, one major challenge will be that of avoiding the temptation to maximize pleasure in the short term (thereby risking greater difficulties over the long term, not to mention possibly violating the cognitive autonomy of many).
Consensual Memory Softening, Memory Erasure, and the Implications of Each
Some research suggests that perhaps it might be possible to use beta blockers to reduce the impact of traumatic memories (such as those one might form while fighting in a war).
While the situation here is different from that of memory erasure in that the memories themselves remain intact (and presumably, treatment would be consensual), the concern that perhaps drug treatment might contribute toward the "dehumanization" of soldiers is not one that can be summarily dismissed. Acts committed within the context of war are often quite horrendous, and it seems that a better world would be one in which these acts never happened at all rather than one in which they are simply accepted as necessary (and in which those likely to experience them are chemically altered in order to lessen their impact).
But at the same time, it does not seem very ethical to condemn people who have experienced terrible trauma to suffer as a result for the rest of their lives if that would indeed be the result in the absence of pharmaceutical therapy. Certainly, there is something to be said for taking bad experiences in perspective and learning from them, but it is probably not very rational to expect that a person in the throes of unrelenting nightmares and flashbacks is going to have much mental energy left over for analysis (and application of whatever realizations come as a result of this analysis). If drug therapy is used for PTSD, care must be taken to assure that the drug's action is used to bring the patient into the sort of space that allows coherent reflection, not a space in which he or she ceases to care about what they experienced. The desire for people not to suffer is not, in and of itself, a bad thing, but the means by which this lack of suffering is achieved must not be heavy-handed or likely to present opportunities for abuse.
But back to the issue of memory removal, since while some of the rationales for the "softening" of memories might resemble those employed in fiction in favor of the outright erasure of memories, there is a distinct qualitative difference between having a memory and not having it (regardless of the emotional impact it maintains over time). One interesting treatment of this subject in fiction is found in the 2004 film, Eternal Sunshine of the Spotless Mind. In the context of this film, memory erasure is consensual and self-directed as opposed to being imposed upon people against their will (or without their knowledge). The characters in Eternal Sunshine know what they are getting into when they enter the memory-modification clinic -- or at least, they do until the treatment has been completed. Memory modification, in the context of Eternal Sunshine is (as observed in the Slate article The Science of Eternal Sunshine by Steven Johnson):
...just the next logical step up from breast augmentation and Prozac. When Clementine (Kate Winslet's character) first decides to shed her memories of Joel (played by Jim Carrey), she does it "on a lark," the way you might get your forehead Botoxed on a whim.
The memory-erasure technology invoked in Eternal Sunshine is described as follows in The Science Of Eternal Sunshine:
The emphasis on feeling over data processing puts Eternal Sunshine squarely in the mainstream of the brain sciences today. We now know that the brain stores emotional memories very differently from unemotional ones. Negative emotional memories, for instance, tend to capture more details about the experience than positive ones: You remember the general feeling of a nice day at the beach, but you remember every little detail of the two seconds when that Buick crashed into you back in high school. Particularly traumatic memories appear to be captured by two separate parts of the brain: the hippocampus, the normal seat of memory, and the amygdala, one of the brain's emotional centers. People incapable of forming long-term memories thanks to hippocampal damage can nonetheless form subconscious memories of traumatic events if their amygdala is intact.
The premise of Eternal Sunshine is interesting in its application here because it takes what is frequently a tool of domineering, evil, high-and-mighty, or desperate characters in fiction and puts it in the hands of regular folks simply looking to customize their lives. In a sense, this is an interesting commentary on the decline of fearmongering that occurs when new technologies with the potential to shake up long-held human "identity constraints" move into the mainstream. Everyone is afraid of something until the neighbor down the street starts using it, at which point it becomes a commodity rather than a horror. Contraception, in-vitro fertilization, and antidepressants have all been through this process -- and while certainly any of these things might be used unscrupulously by powerful agents toward unfortunate ends (e.g., through coercive sterilization of the disabled, or through inappropriate administration of medication for the sake of keeping patients subdued), most present-day uses of these technologies are consensual and matter-of-fact. Could something so extreme as memory deletion ever reach this status, provided it ever became possible?
It is this writer's assertion that memory modification to the degree of actually erasing all traces of the effect of an event is both unlikely to reach the status of birth control and Prozac, and probably impossible in the first place. The unlikelihood of the mainstreaming of "memory erasure" is closely tied to its probable impossibility, which exists not necessarily because of anything fundamental about the brain, but because when an event happens, it generally affects more than one person. It also affects inanimate objects, the environment, and numerous other variables that may get taken for granted at the time but that almost certainly leave the indelible mark of the event upon reality.
The memory-modified person's life since the event would then have to be re-framed in the context of the trauma not having happened -- something that seems almost guaranteed to result in severe cognitive dissonance. And then, of course, there are the logistical considerations to keep in mind. A person would have to somehow destroy all references to the event, including his or her own writing about it, and including any press articles that referenced it. Additionally, that person's loved ones and friends would either need to have their memories erased, or they would have to avoid mentioning the event forever (an unlikely scenario, since humans are notoriously bad secret-keepers). Most people are not absolutely alone when a traumatic event takes place -- abuse requires an abuser, and war requires two sides (and generally, teamwork). Removing a memory from only one person, even if it were possible, would still leave others cognizant of the event. Couple all that with the increasing societal move toward participatory panopticon, and you have a situation in which the task of expunging an event from all record, everywhere, is more than merely daunting. Altogether, memory deletion seems as if it would be too much trouble to bother executing even if it were possible.
Additionally, it is worth asking the question of what rationale a person might use in favor of choosing to deleting a memory instead of simply lessening its impact. While memory-softening agents certainly change the story of a person's future by allowing them to take their negative experiences in greater stride than they would have otherwise, memory-erasing agents have a more curious power -- that of being able to change the story of a person's past. It seems as if different personality types might find this prospect either very attractive or very repellent -- people with a strong tendency toward "editing" their past (and it is thought that we all do this to some extent) might be receptive to the idea of being able to make their memories of self match their idealized self, but people who prize truth and consider their past experiences to be fundamental in shaping who they are would probably stay far away from any such technology.
It seems that the diversity of ways in which emerging or future technologies might be used will be as diverse as the set of personalities currently in existence. But in the case of memory modification (or memory deletion), it seems very likely that the existence and widespread use of this technology will be discouraged by (as mentioned earlier) participatory panopticon and the availability of memory "softening" agents that can keep memories intact without requiring that they continue to torture those who recall them. And as far as those who would simply rather not remember certain things that happened (for what amount to cosmetic reasons), so far, having the ability to remember poor choices and faux pas has not stopped people from denying them anyway.