so in a subtoot @alice said
I should specify that I mean "moderated registration" not "invite-only" or "no signups" when I've been saying closed registration here.
[edit for correctness] and in parallel you said:
I say this from experience. I remember how online forums tried to handle spam, bots, and trolls — by making registration harder. Some required manual review or moderator approval. That worked for a while, but it also made those communities less welcoming and more difficult to join. Over time, most forums faded away.
and, Netscape, I think you're not really doing the math well here. Alice has pointed out it takes them on average less than a minute to vet a new account application. It takes longer to write - but if a user can't be bothered to write a paragraph about themselves asking to join a server, are they really going to contribute to discussions? It is not gatekeeping. It is not onerous to have applications take a day to approve.
More importantly, it is not "less welcoming" to have a policy of no bad actors. It is more welcoming.
The sign up friction is not a concern in this way, and in fact is likely positive as there are studies showing that paying even a nominal amount of money or energy for a thing makes a person value that thing much more, which implies much greater stickiness, if growth of actual community members is your goal.
(Growth of new signups who never post should not be your goal.)
So.