Why not HTTP headers? (Score 1)

As it has been noticed, auto-censorship can only work if you have some kind of uniform international legislation. If you assume that possible, then it may be simpler to have the porn sites add some extra HTTP headers, like

X-Porn-Level: hard-core

This way every user (publicly financed or not) would be able to choose the level at which he wants to filter out.

Sure, a precise definition of the levels would not be easy, but at least it would give you the possibility of not putting explicit sex and simple nudity (like in erotic paintings or photography) in the same basket.