I think clothing primarily came as a way to protect sensitive areas from the elements. Primitive man started wearing loin cloths to protect their reproductive areas from anything that might be a danger to them. Go forward tens of thousands of years, and people start wearing clothing as a sign of social status. Nowadays, I think the main the main reason is because its always been that way. Because of that, we have come to see nudity as obscene, even though it isn't in the slightest. Modern society is also a bad influence to our children, teaching them that the human body is a bad thing.
It really is detrimental to our society, but it is not going to change anytime soon.
On a somewhat unrelated note, I feel this thread would be more appropriately suited (no pun intended) to the Mature Discussion forum.