> The kids already know how to use VPNs to circumvent firewalls

Vpn is not always a solution, at least in my experience (nordvpn).

I haven’t tried 4chan, but e.g. reddit rejects anonymous vpn traffic (shows an error message, forces login); streaming platforms also often don’t work.

4chan has a rule banning use of proxies/VPNs and enforces this with IP range bans.