Why do people think nudity is bad?

A lot of us think of nudity is good and healthy. Even with the cultural pressure, most people seem to be OK with it themselves but they don't care to buck the cultural taboo. Have those same people stumble onto a nude beach, sauna, or communal bath in another culture, and they quickly become comfortable with it. In other words, if people knew that others aren't as hard over about it as they think they are, it would be more accepted.