A sane anti-porn law would be that sources have to identify any porn, with a tag or a http header or something like that, or face a big fine.

There are systems for this. If and whether they are followed, I have no idea. I imagine porn sites would follow the law if it's not too inconvenient for them. But the other random sites that kids are going to be reduced to finding porn on are going to be harder to censor.

Um, anyways, that effectively makes the government the determiner of what is and is not porn, the evasion of which is kind of the point here. It's much better to have a web of voluntary systems. It will work better, and we're not going to disable the whole internet to keep kids off porn. Solutions have to be reasonable.