If a website chooses to spam you with porn adverts, popups, etc, I think that's their prerogative...and there is really nothing a third party can do otherwise. Otherwise, if you're talking about email spam pointing toward a particular porn website, sometimes you can go to the affiliate company and complain, or the emailer host (though most emailers are zombies these days).
If they send you email, then you could complain to their host, for most hosts spamming is a definite nono and they run a serious risks of having their account suspended. If it's pop-ups on their site just stop visiting that site.
Bingo. It's a huge problem. This is why I'm all for having black hole organizations and the ability to filter out all traffic from certain locations, including countries, if that is what you have to do.