We all exist in a society and (as the other comment says) it take society to raise kids. I don't want a society where as a parent I have to fight against shitty parents and the potential immaturity of my kids (they are too young right now thank god) to stop them watching porn as a 11yo or other inappropriate gifts from internet "culture".
Setting some reasonable standards for what content kids should consume provides parents with cover when trying to raise their children well. Its the reason movies have age gates, and strip clubs and many other things not on the internet.