Well I do have an answer for that one, from personal experience I know that being introduced to sex/nudity as you call it DOES INDEED mess up a kid, unlike animals we tend to look for an explanation of things to understand the world that surrounds us, an animal can see it's "parents" having sex and it does not have consequences...a kid will start wondering the "what", "why" and "who" of everything.
If I could go back in time I would prefer NOT to have known anything about sex until I turned 12 or 14...
Even if some relate it to a moral or religious connotation it is absolutely preferable to keep a kid out of the loop until he/she is ready to understand certain aspects of human behavior, its origins and consequences.
And just FYI, violence is ok only if it is done in a funny (three stoogies) way, remember Donald Duck or Bugs Bunny? Today's violence is so much different, therefore as parents it is our duty to cover our kids ears and eyes when something crosses the line.
And as djsatanwife said "making sure he knows its fake"...THAT is uber-important...