The idea is that society should have some common standards for what's inappropriate for children. For example, parents don't want their kids to buy cigarettes, but also, stores don't want to sell them cigarettes. When there's consensus on this, cooperation is possible. Parents have an easier time when they get cooperation from the rest of society.

But there isn't going to be consensus on everything, so content filters are still needed.

So simple, just get various Christian, Muslim, atheist, traditionalist and progressive, sane and insane parents to all agree on a common set of what is appropriate and inappropriate. And then enforce that on all of their children. Why didn’t I think of that? That should go great.