I'm sorry to say - but that is a very dysfunctional home they have there. The fact that your mother knows full well what goes on, and let's him get away with it.
It's a complete addiction, and people are correct - it is only going to get worse. Studies have shown that it takes more and more, to get the desired effect -- just like a drug. I am willing to bet that your mother and father don't have much (any?) of a love life. Maybe this is why she doesn't object - it keeps him away from her?

At any rate, none of that matters. What matters is that your son and any future children that you have, are not safe around your parents. I'm not even sure I'd trust them when I was there -- as your son gets older, you won't be with him every step.

Truthfully, even if I didn't have kids - it would creep me out to be around this guy. But then again, this has gone on so long, with nobody complaining. He has gotten the message that it's perfectly ok. And of course he thinks it should be, I'm sure, as it is his house - and no matter who is there, he believes he has every right to do what he is doing, basically right out in the open. I totally agree that the idea of people knowing, or being "caught" is another aspect to what he enjoys about all of this. So whenever you set foot in that house - you are basically becoming part of his addiction. Ick. Knowing that - I would tell them both, nope - never coming again, unless he gets help, and that stops. You're perfectly in the right to do just that, even without your child.

And I also have to add that I'm not really against p**n. But there is a time and a place. And I do know that people shouldn't use it compulsively, that it does create an escalating need, if it isn't kept in moderation and within certain boundaries. (As in, use by couples together, or use very sparingly)

I'm sorry that you are going through this. Very sad - and especially because both your parents seem to want to act like it's normal. It is so not.