That's a much better approach in general. It's much easier to regulate and enforce that websites must expose these headers so that UAs can do their own filteri

That's a much better approach in general. It's much easier to regulate and enforce that websites must expose these headers so that UAs can do their own filtering. Adult Content = headers in response, no ifs, ands, or buts Response headers are encrypted in the context of HTTPS, so there's no real sacrifice in privacy. Implementation effort about as close to trivial as can be. No real free speech implications (unless you really want to argue that those headers constitute compelled speech). All in all, it's a pretty decent solution.