Nothing. What consenting adults do in private — what movies they watch, what books they read, what they do for recreation — is nobody else’s business.
That's not entirely true, is it? People get arrested for child pornography all the time. And don't tell me its legal to smoke pot or shoot crack if you do it in private.
But let's leave the extreme cases out for now. Here is a scenario. A man rapes a woman. This is the first time he ever raped a woman and he is caught. If the man is found to have porn movies with rape themes in his possession, it can be used by the prosecutor to show a pattern of behavior that this person is maladjusted for society and deserves to be locked up for a long time.
The point here is that what you do in the privacy of your own home will tend to leak into every other aspect of your life. If you are addicted to porn, there is a good chance you will be caught watching porn at work. If you are addicted to gambling, you will eventually hurt somebody, whether it be you or your family. Normal human beings tend to not be very good at completely compartmentalizing different aspects of their lives.
Shit. There goes my 1970s soft-porn fantasy, “Swinging Tennis Chicks.”
hmm... that WOULD be an interesting porn. Think what they can do with the rackets.