Chests 'baring it all'

I've been wondering this for awhile, but why exactly are places like here, VoA, ect or even for that matter some image boards ect. afraid of posting little girls topless and freak out about the idea of flat chests "baring it all"? To me personally chests, breasts, nipples ect. regardless of age I don't see the point in covering up. I really don't see why people view chest region as being sexual either. I also don't get why people get offended by the ideas of breast-feeding in public ect ect. I mean christs sake that's what breasts where invented for! (duh WE ARE MAMMALS.) Can someone explain to me why people think that breasts are strictly sexual, and need to be covered up and are offended by seeing them in public? Society confuses me....