The justification for banning possession of child pornography was that you could draw a straight line from the images to an act of exploitation. The reason for the laws is not primarily to prevent the spread of the images; it's to prevent the exploitation of a child that lead to their production. When you have teenagers voluntarily snapping pictures of themselves, there is no act of exploitation. Sure, it's not something that should be encouraged, but it's not something that should destroy your life, either.