What about the Marxist-Leninist, communist, socialist, anti-capitalist crowd? I don’t know if they hang around on other platforms, but they certainly are present here on Lemmy.

Also, what about sexual and gender minorities? I get the feeling that there are a lot of queer people on Mastodon. Maybe that could be another selection criteria.

Like this:

Are you queer? -> Mastodon

Are you a Marxist? -> Lemmy