This shame and guilt about the body causes all sorts of hangups about the body, including sexual issues. This knowledge helps prevent self-consciousness, and it fosters respect for other people. It's important for children to KNOW what the opposite sex looks like, and not grow up perpetuating the nervous, intense mystery and mystique about the human body. Keeping bodies from view causes a lot of sexual deviance in our society. It's also important for children to know first-hand what changes happen in peoples' bodies at puberty, rather than, again, speculate and worry about those changes.
Social nudism promotes a healthy self-concept.
Nudists are from all socioeconomic backgrounds and professions. They are your neighbors, your co-workers, your friends, etc. There are many more things I have learned, but that's a sampling to whet your appetite. Check out my links that follow, the first two of which are extremely valuable on this subject. These websites will shed some light on why this nude stuff is so beneficial.