I think this falls into one of those social problems with no technical solution. The culture of PGP, as described in the post itself, is that anyone can partici

I think this falls into one of those social problems with no technical solution. The culture of PGP, as described in the post itself, is that anyone can participate, anyone can upload signatures, anyone can run keyservers, there's no way to remove uploaded keys or signatures ever, and there's no central authority for what is on the keyserver network. Given that culture, there's a social expectation that if you're not going to let the pedophile with the anime avatar have the rest of his arguments taken at face value, you're censoring people and might as well go use one of those corporate sell-out encryption systems like Signal. (To your actual question: meta.stackoverflow.com, Wikipedia talk pages, meta.wikimedia.org, etc. Also various email/chat communities have defined off-topic lists/rooms. When the participants do actually want to keep off-topic discourse to the side, and the off-topic discussion isn't an attack on the competence of someone reporting a problem or a desire to propagate child pornography, then it's merely a technical problem of enabling them to do it.)