I have read the book but skimmed wikipedia's summary of it. I have also seen a lot of real patients with psychiatric illnesses. Based on these things, I have therefore come to this conclusion and interpretation - Bateman shows no signs of insanity (other than at the end when he had a visual hallucination of the words 'feed me a stray cat' and therefore in my eyes he is not insane but a 'normal' product of capitalism. I believe that the film is trying to show how greedy and blind rich people can be - to their own needs, to their souls, to others, and therefore they are suffering (as well as everyone else they 'kill' and the sad thing is no one else can realise it but poor people like the chinese cleaner and the hooker's friend. Such greedy people, as represented by Bateman, are aware of it but try to suppress it - they would even go to the extent of killing eachother (not literally but at least they are killing eachothers souls with all the greed, envy, superficial opinions on eachothers dress sense, relationships, envious efforts to be better and ironically therefore hate other people showing off/having better than themselves etc). They are not aware of the signs of eachothers sufferings - e.g. the blood on the floor was ignored and the body bag was praised as 'a great bag - where did you get it' and Bateman Zombie-like replied back the store he got it in. But no one looks deeper - whats in the bag? whats behind the suit? what's the quality of the food you are getting. Poor Bateman tries to break-free from this because at least he is aware of the insanity as he is aware of his own insanity and that he bubbling up inside and he also commented in the resturaunt to Paul that it served nice food but this wasn't good enough for him. So really, Bateman could not survive being in that environment without harming someone due to competition and ended up hurting his fiance and almost hurting his poor secretary. But he managed to warn them and so that is at least honorable. So, whether or not he truely did kill those people or not doesnt matter - people have the potential to kill eachothers souls, ambitions, careers, etc all the time and people do it all the time and that is real enough. Bateman at least was trying to seek help and his culture didn't allow him to get the help he needed because they kept suppressing it as normal - which is represented by in the last scene.