Mary Harron knew American Psycho's music had to set the tone

In an Ask Me Anything (AMA) on Reddit, Bret Easton Ellis explained why he referenced the music and artists he did in "American Psycho":

"In a lot of ways, Patrick's rants are about wanting to fit in with a society he doesn't believe in. That's also where I was. At the time. So a lot of the rants came from also of my frustration I didn't like any of the music that Patrick liked, but it was popular at the time and it seemed to reflect a certain type of mass taste that [Patrick Bateman] wanted to be a part of."

Speaking with Little White Lies, Mary Harron said she thought the musical choices in the book were perfect. After all, they weren't just satirical picks, their upbeat beats would (and did) create hilarious audio/video contrasts. So, Harron decided she couldn't change the film's music, no matter the cost:

"It was really hard to get the rights for the music because we couldn't find anything that worked as well as the music mentioned in the book. It had to be brilliant, mainstream pop. More the music was happy, the better it worked [...] It had to be American and it had to be upbeat."

That meant Huey Lewis and the News, Genesis and Whitney Houston were key for the soundtrack. The film also added "Walking on Sunshine" by Katrina And The Waves, the ultimate sunny song of the 80s. There is also a nod to Michael Jackson when Bateman walks on the moon (badly) before killing Paul Allen (Jared Leto). As Harron said, that last touch was Bale's suggestion.