Why is it that some people don't like animals?

Hi, I'm just curious as to why some people don't like animals? I know some people who aren't big animal lovers, but they would never inflict any pain on an animal, and they'd never allow anyone to hurt an animal, but I also know some people who would gladly hurt animals because they hate them so much. These people have never had any bad experiences with animals, so why is it that they hate them so much? is it to do with genetics? or their upbringing, or is it something else entirely? A bit of an odd question, I know, but I'm very curious :P