I'm always fascinated when I hear people say this. My good GF and I have this disagreement, as she is of the position that children shouldn't be "cloistered", I think that most sane people will agree that there are limits on what kids should be exposed to, (porn, drugs, violence for extreme examples of the things that are out in the world and available, but most people wouldn't take their kid to a strip club to make sure he is not missing something
) so its simply a question of what the line should be and who is in the best position to determine for their own child.
I don't think the icky stuff out there works like a vaccine, you know give him some now and it will protect them later. The ick will still be there if when he gets older its what he chooses to indulge in, and he is willing to deal with possible consequences. For now, for these all too fleeting years, its my job to protect him....just as I wouldn't risk his physical harm (after all, someday he could get hurt and will need to know what its like), I strongly believe that protecting innocence is just as important. Life is ugly.....he'll find out all too soon that people can be hateful, no need to rush him......