THe government shouldn't be raising anyone's children, that's what parents are for. If you're a bad parent, your kids will get access to bad things and could become an adult failure. The future of your family and your legacy is up to you, not the government. We don't need age verification to restrict the social darwinism of raising children.
Maybe we need to turn it on its head, point out that if we want legislation to help out with this, we could choose legislation that gives power to parents. Age verification laws put the power directly into the law itself, they're a blanket solution that gives all the power to legislators and that prevents parents from making decisions about what's appropriate for their kids and what isn't.
If the market isn't delivering the level of parental controls people want, then sure, maybe legislation is needed. But it should be legislation that improves parental such that parents can make decisions about what's appropriate for their children.