TheMotte [0] is pretty good. It's explicitly about long form argumentation about any topic really. It was originally a subreddit and stemmed from the Slatestar

TheMotte [0] is pretty good. It's explicitly about long form argumentation about any topic really. It was originally a subreddit and stemmed from the Slatestar Codex community I believe, and then they made their own forum. The discussions are pretty interesting, ephemeral even, but if you hang out, you soon learn who the regulars are. [0] https://themotte.org https://themotte.org