I've been with large groups of people who were skinny dipping. Nobody really cared about what everyone else looked like, they were busy having fun swimming and just spending time with people who didn't judge. At least half were morbidly obese and no one made comments about their size, everyone was welcome. I think naturalists have a different way of looking at things than most people.
Religion and the beauty industry are the ones who have turned being naked into something shameful. I think one of the problems people have with it is that they equate being naked with sex. Once you can separate the two, you aren't so worried about what you look like or about having to impress others.
Of course there are times when it isn't practical to be naked, we wore towels around the food.