This nonsense was tried back in the 1980s...
... when it was decided that access to the 0898 "naughty phone lines" should be made opt-in rather than opt-out.
Unsurprisingly, very few people were willing to call up their phone provider and say "Please let me access the smutty message services", meaning that perfectly legal and legitimate businesses suddenly had a massive drop in their income.
Eventually, of course, this decision was reversed, but it just goes to show how stupid the "Won't Someone Think of the Children!" mentality can be.