This was a pleasure to read. An important topic, good insights, well written. I am just saying this because I feel this deserves more positive feedback than mere upvote, but I have nothing substantial to add on the topic, because it feels like you have already said it all. :D
I specifically like the three questions (Is this person's presence a net positive or net negative for the group? Do I actually trust this person? Do I actually like this person?), because that seems like a sufficiently simple rule to actually use, and could help to avoid some problems.