This is a Doctor Who post. These are totally my favorite kind of posts, you know. Also, spoilers. Amy Pond's journeys with the Doctor have been a central part of the narrative of series 5 and 6. There have been plenty of recurring themes throughout her time with the Doctor, but I've just noticed that one in particular neatly bookends her adventures, and crops up a few other times in between.
Amy and the Doctor pointedly disagree on the ethics surrounding memory, and this disagreement highlights the perspective differences between a deontological and consequential ethical system.
Amy appears to believe that the moral value of an action is contained within the action itself -- for example, she still holds herself accountable for murder (or, at least, for deliberately allowing someone to die) in the alternate universe in the season finale, even though it never happened. And in the second episode of series 5, she can't imagine how she could be held accountable for her actions in the voting booth, when she tried to persuade the Doctor to leave Starship UK, because her memory was wiped of the event, so she lost the perspective basis on which she judges the value of her actions.
This quality of her perspective also crops up in the Doctor's death scene -- she feels she has to do something about it, because it's not about whether the Doctor should or shouldn't die. It's about whether she did, or tried to do, something. In "The Girl Who Waited," she and Rory (more Rory, who was there for the event as it occurred) obviously have a problem with having abandoned older Amy.
The Doctor, on the other hand, is a fairly strict utilitarian -- to his mind, the consequences of an action are the only thing that determines its moral value, and that value is determined by whether it causes suffering to conscious beings.
In "The Beast Below," he doesn't care that Amy doesn't remember choosing to try to get him off Starship UK. He cares that her decision made it more difficult for him to save the star whale. And in the case of older Amy, he doesn't feel a wrong was committed because the second Amy will have never existed. This view has also apparently rubbed off on River Song, who consoles Amy that she didn't commit murder because the timeline in which the murder took place didn't happen.
If you haven't already guessed, I think the Doctor is right -- it matters what happens as a result of what you do less than it matters what you did in the first place.
Talk to you tomorrow.