Kbin is a part of the Fediverse and is similar to Lemmy. I have a kbin.social account and am replying to you from kbin. (I subscribe to a lot of Lemmy communities via kbin).
Tildes is not a part of the Fediverse. It is a text-driven private forum basically created and run by one person. You need an invite from a Tildes account holder to join. It's its own little island. am on Tildes a lot and really like it.
I deleted all of my comments using PDS. I just did a Google search for my username on Reddit and it had one result. I went to the post (I remember the OP) but my comment doesn't appear on the post. So is this a caching issue?
Early adopters of any innovation likely have certain personality traits that make them able and willing to assess a new technology and learn/overcome some obstacles to use it. Maybe those traits translate into pleasant, respectful online communication?
ETA: I need to see if I still have my old grad school copy of Diffusion of Innovation. It might have some answer in there.
The FIRE community could use the existing Mr. Money Mustache forums. Only hiccup is, I believe, that it is difficult to get a new account (not sure why that is, maybe that's an old problem and it's easier now). I've lurked that forum for years; they seem like a friendly, helpful, well regulated, un-frothy bunch.
There is a thing called Reputation (IIRC) tucked away in your profile. Im not sure if that's a true karma equivalent. Also not sure what you can do with it.