Gay men too, and straight women specifically
While I doubt that you'd be surprised by this observation, many people are simply terrified of nudity. Many clearly believe it has a negative impact on society and far more so than violent media.
I think it often boils down to feelings of jealousy (is my husband/wife/girlfriend/boyfriend/whatever more attracted to this naked person/image than me?), insecurity or personal feelings of shame and guilt.
Years of social conditioning, usually by very conservative communities tend to have that effect. And we all know how screwed up conservative communities often are and how they negatively impact society at large.
All the same... Nudity FTW. People need to get over themselves. Don't like the media? Don't engage in it.
Although, truth be told, conservatives tend to foster the notion that they need to be told what to do, how to live, what to like and what not to like. So advising "Don't like it, don't watch it" is a lot like telling someone with a chronic addiction (read: obsession) to simply "get over it."