Why is naked either great or awful?

It seems like with most people, seeing someone naked is either great or disgusting, but there's never a middle ground. I know it's based on whether you're attracted to that person or not, but why is it gross until a person gets to a certain level of attractiveness, than automatically goes from gross to awesome sexy? There's no gradual changeover in one's reaction to someone naked on the attractive scale. Am I making sense? It's the same kind of scale on kissing someone, it's either fabulous or horrible, no middle ground.