most people who use the internet would not have an opinion about this. In fact, a huge chunk of internet users seek out and frequent porn sites. Non-porn webmasters may see it as the 'dark side', but users love it.
It aint spam. It's one of the core reasons for internet adoption, usage and participation.
Forcing adult material onto a single extension is a dangerous, big-brotherly, we-know-best kind of attitude that will make it easy to start implementing all kinds of censorship and standards on both porn and non-porn alike.
Oh, you have profanity on a couple of web-pages? you have a picture of someone's breasts? Well, what are you doing here on a regular TLD? Kids could be reading this stuff! "Move to a .xx or take it down!"
Trying to introduce such a measure demonstrates the belief that there is a problem. Well, there is no problem. The only problem is that there are vast amounts of porn online, and there are millions of people going to those sites every minute and watching the porn. If that offends you, then maybe that's why you want to curtail this "problem."
Frankly, I think internet porn is one of the best things that could have happened to the world. Sure, it is often tacky, tasteless, mediocre, and disgusting.
But you can't maintain the rage when you're looking at porn. Maybe the war-torn parts of the world need to distract all of their unhappy, angry, frustrated young men with truckloads of porn. It's hard to get the motivation to go and kill people when you've got a massive gallery of your favorite links in front of you.
It seems like no coincidence that those who wage war do not look at porn.
I'm going to get a bumper sticker: "no .xx extension please".