Do straight guys feel uncomfortable / repugnant for sex with effeminate guy ?

I know a few gay guys, have gone to gay bars with them and met their gay friends. A few gay guys I know are married or have been together for some time. I must be straight as an arrow because I can never figure out why a guy would be attracted to another guy. I have tried to reason it out in my mind and put myself in their shoes but I can't.