The orthodox Jewish religion has a ban on just about any nudity at all. They cover their upper arms, shoulders, legs and hair, in the name of modesty.
Now, I don't know very much about Judaism, but I do know that it shares the Christian Old Testament. Now, I don't know much about Christianity (actually, a fair bit) but I do know that in the very first chapter (Genesis) the first man and woman start out in paradise not wearing any clothes. After they eat from the tree of knowledge/evil, they suddenly realize their own nudity. They put on fig leaves (so the story goes) to hide their naughty bits. God finds them hiding, and kicks them out of paradise.
So what? Well, like the wonderful webcomic Indexed, I will explain this using a graph:
We can see quite clearly from this graph that amount of paradise relates very strongly to how much clothes are worn. Therefore, all that "modest" people are doing is trying to escape paradise. Why they do this, we can never truly know - is it because they are insecure and don't think they deserve paradise (or insecure and think they're ugly)? Is it because they believe that since "they" ate the forbidden fruit, they don't deserve paradise (or since they ate at MacDonald's too much, they don't deserve to be nude in public)?
It could be anything! It's impossible to say.
Beyond the simple paradise versus clothes comparison, one can observe how God "made us in his image" and that therefore we're covering it up! Why would he want that?
I'm not sure exactly what I think. I can't say I'd like the whole world to suddenly turn nudist, but I guess I wish it had been that way when I grew up.
Or maybe I'm just a Naturist...