
It's not about the humor of the post itself at that point, it's about the dynamics of power and control. Those posting that shit get more of a kick out of the feeling of power they get when they see they've had an effect on another person, than they do from the joke itself. It's an impish and antisocial impulse.
The FBI has visual evidence of all of these people committing crimes. You can literally find thousands of pages with “no image produced” because its illegal to distribute such horrific imagery. You can comb the files yourself, or watch video analyses on your own, but you’re a pedo lover, so I don’t expect you to.