Can someone please explain the ending of "American Psycho" to me?

you answered your own question IMO. THis is a brilliant film and it is meant to be an ogy of society. The business card scene is truly one of the top scenes of filmmaking. Christian Bale is such a precise actor, even when he was a child, he genuinely almost becomes the character. He almost has too much heart to play such a living dead manas Bates. The way he arranges his features into a mask of apathy...it's chilling. In fact the only time he feels anything is when he is killing, hence his need to do so. But yes, in the story he really was killing people but as you said, nothing actually happened as a result of it due to the general disinterest of people. Sadly that is all too accurate a description of modern culture.