It's stupid, obviously, but some are protesting the creation of a .xxx upper level domain because it might cause more porn to be posted on the internet. This, of course, follows the same logic as saying that legalising marijuana would cause everyone to become a pothead.
Porn is a commodity which follows the laws of supply and demand like any product or service. As long as there is a demand, someone will be there with a supply. Whether or not the consumer gets it at www.dirtywhores.com or www.dirtywhores.xxx is entirely irrelevant.