You're equating seeing nude bodies in non-sexual environments with viewing explicit sex scenes. These are incredibly different. A more apt comparison would be if you & people in your culture regularly met to hang, talk, etc in brothels/sex clubs.
Would you be comfortable being around strangers that were having sex right next to you?
Edit: Nudity isn't an inherently sexual thing. Sex, by definition, is a sexual thing. I'm certainly not saying sex is shameful or immoral, but it is different, and one can easily believe/argue that nudity is fine while sex should be kept private (fade to black in non-porn games).
