Consider what happens if you have a community that is very nice, very trusting, and open to everyone including complete strangers who behave weirdly.
At the beginning it can be a nice place. Until the first abuser finds them. And then... depends on the abuser.
This is not a theory; I have seen it happen, often in groups of nerds who are somewhat naive about how real life works. Then a new guy comes, borrows some money from each of them individually, then disappears. Or a new guy comes, invites a girl to his place, and rapes her. Sometimes some people even get suspicious about the new guy, but is a taboo to express such thoughts loudly, to spread suspicion in a group based on mutual trust.
To avoid things like this, you need to split people into "those I trust" and "strangers". Different people and cultures draw the line differently. For some of them, "those I trust" only includes people they have known for a few years. It is frustrating for a newcomer, and you often wish you were able to do something so that they accept you faster. Unfortunately, if that worked, the abuser would probably do the same thing.
Another strategy is to have mutual friends vouch for someone. But this only works when it is a part of the culture, where people know that vouching for someone brings heavy consequences if that person turns out to be an abuser. In cultures that do not have such experience, abusers often do the trick where they befriend someone, use them to get introduced to their friends, and while the first target is like "this is a nice stranger that I have met yesterday", their friends are like "this is a nice person recommended by my trusted friend, which means I can trust them too", and then the abuser exploits them. (And when they complain to the first target "why did you make me trust such a horrible person", the first target is confused "well, I actually barely knew them, this was a horrible misunderstanding". But the abuser probably has a lot of experience creating such misunderstandings on purpose.)
Finally, you can have a close community that is very difficult to enter. You can trust everyone in that community, because if they do something bad, they will be kicked out, or worse. But this requires the community to be very difficult to enter, and to have ways to punish the abusers in a way that actually hurts them. (Merely kicking someone out of the community is not enough, if there are hundreds of communities, and the abuser simply infiltrates the next one.)
Abusers exist. You need to build a firewall somewhere. There are different places where you can build it, but you have to build it somewhere, or you get hurt.