People on HN always seem to misunderstand the point of these measures.

They're not there to make it impossible for anyone under the age of 18 to ever see pornographic content. They exist to make sure that porn isn't pushed at children who don't want to see it. It wasn't that long ago that pornographic ads were common on some ad networks or in email spam. It's this accidental stumbling upon porn that the measures aim to stop.

The blocks are always described in the strongest possible terms by the politicians pushing them because:

1) It makes the public think politicians are taking strong action against poor behaviour

2) It gives the politicians a stronger bargaining position: implement good voluntary age restrictions or we'll put in place a stupid filter.