Attempt at an honest answer:
If a group has been marginalized, belittled, and excluded for long enough, it can damage the people in that group. They can need a safe place to heal, to realize that they matter, that they are as worthwhile as anyone else, and that they don't have to be what their oppressors said they were. A safe place can be very important in that process.
Or a safe place can be a place where a bunch that feels oppressed because somebody looked at them funny, and feels more oppressed because nobody else thinks they're oppressed, can get together and rehash their sense of victimhood and exclude anyone who disagrees.
Human nature being what it is, the second is perhaps more likely than the first. But that does not make the first invalid (when genuinely needed).