Boy, I totally saw this film differently than the majority here. Of course, I haven't read the book which might be an influence on interpreting the film.
With that in mind, I thought the whole point of the ending was that Bateman turned out to be a bitter, hateful and totally ineffectual person completely incapable of acting on his own behalf. It's this very fact that fuels his murderous fantasies. They are his only outlet and are so violent because he needs to make up for so much inability in reality.
In his world, all people are shallow (he perhaps most of all) and self-centered. Everything is measured in status, yet the people with status control this world and deny any others access to more status. So Bateman has nowhere to go. He is stuck being a nothing in a world where that is the worst possible thing you can be. If he only had some human outlet where the inner-person could matter (like with his secretary) then he could find comfort with himself. But this idea is totally alien to him.
His facination with bland, VH1 music that he sees as sweeping across all genres while it really is a very small, focused style tells us more about the shallowness of his emotions. Think of High Fidelity in which Cusak tells us that he and his friends judge others by their taste in art (primarily music). Bateman's musical tastes tells us of his complete shallowness, and his pontification on these artists tells us that he is unaware that he has such simplistic (and safe) tastes.
So, not unlike the Columbine kids or so many other "oppressed/nerdy" people turned killer, he looks for his only chance at "power" by killing. But rather than give the character some sort of satisfaction and in some way "verifying" his outlet as reasonable at least in terms of being empowering, we find that even in this arena he can do nothing.
He is a frightening, hateful "Walter Mitty" with "big" dreams but the utter lack of inner-strength to accomplish anything, even murder. In the end the audiance sees him as pathetic, yet can hardly sympathize with him either.
I thought it was a viscious (yet needed) attack on this shallow Wall St business-yuppie lifestyle. I would equate it slightly in themes with "A Place in the Sun", which I saw recently, except in that film the one person who is "alive" is outside this lifestyle trying desperately to break in, and is therefore actually capable of such a crime.
Again, this is what I walked away from American Psycho feeling. Based on this thread I guess it's safe to say YMMV.
he didn't really kill anyone at all. Pretty interesting film, IMHO.
