@alice an excellent analysis

I'd add one addendum for those in the audience who want a low effort policy that's more aggressive

There is another option much more heavy-handed -- toward "innocent" and "guilty" alike. One common to servers including mine:

By referral, after referrer has been registered X months

The number who accidentally invite someone who doesn't share culture and values of the place is very low

And if fedi shows anything imo, it's that this scales better than many think