The American Civil Liberties Union -- and other members of the international Global Internet Liberty Campaign -- caution that publishers speaking frankly about birth control, AIDS prevention, gay and lesbian sex, the social problem of prison rape, etc., could be coerced into moving to an adult domain. Once there, they would be stigmatized and easily blocked by schools, libraries, companies, and other groups using filtering software. Publishers of such information, who do not view themselves as pornographers and retain their existing addresses, could be targeted for prosecution.
Er, forgot to finish that comment. Then forgot what I was going to finish it with. Probably something like "that should work okay" or something. Erm, yeah.
So should socialism or libertarianism. In theory, anyway. When you factor in social dynamics, the "voluntary" part turns out to be a pie-in-the-sky fantasy.
Completely voluntary .sex (or even .porn) for strictly pornography sites; all other sites should be able to go about their business on .net or .org or whatever.