Personally I've never been disgusted by casual sex. It's something I genuinely enjoy and seek out when I'm not dating someone. In my experience, women enjoy it just as much. It's all about being the right guy.
I'm disgusted by STDs, pregnancy, and bad smells. Not casual sex. In theory casual sex is ideal. In reality, people are flawed and have issues and/or things happen, and those things repulse me.
I also always hated the feeling of leaving someone's house after that. It felt like fleeing a crime scene where I just wanted to get the hell out of there as fast as possible and shower off the DNA evidence.
These could all be problems with me. If that's the case this is some mini therapy.