Personally I think that a mans penis or lower body is even more taboo than a vagina and boobs being exposed.
Because when have you ever seen a guy showing his penis in anything? Other than porn or possibly art.
Afraid that your ding dong will stand guard or crawl into the cave?
Well boobs are a little bit less "interactive" with their environments.
I must admit, I don't feel comfortable naked in a place where people can see me, not including of course in a one on one scenario. BUT if I were born in a society where everyone was taught that there is nothing to be ashamed of in your body and everyone walked around naked I bet I wouldn't.
Clothes are useful where I live though, because it gets cold. So they go beyond covering ones self up.
"George Bush says he speaks to god every day, and christians love him for it. If George Bush said he spoke to god through his hair dryer, they would think he was mad. I fail to see how the addition of a hair dryer makes it any more absurd."