If they dont use the .xxx domain, and use .com instead, we can then say they are pushing this stuff on the rest of us who don't desire this, thus perhaps lead on to maybe some legal charges? No one is saying they can't publish, just where they can.
I say establish the domain and make it clear that US law (And other nations will follow suit!)will not punish attacks against porn sites operating outside that domain or allow such companies to debit American citizens credit cards, etc...
The free sites run by non profit perverts will stay, but some of the well-funded folk will head...