What you're describing here doesn't exist on any mainstream websites. On the other hand, there are plenty of women-only or PoC-only subreddits, for example. So while what you're saying is true, I'm not really sure why it's relevant.
> exclusionary
You're creating a false equivalence between two different concepts of "exclusion"; one is actual enforced exclusion (like banning people whose opinions you don't like) and the other is when someone gets their feelings hurt because they don't like what's being said on a website.
> Do you shut up some idiots who have nothing but purely harmful things to say, or all people of color?
You're doing it again. "Shut up" means, in one case, banning people, and in the other case, when they (hypothetically) choose to leave of their own accord because they don't like the community.
It's not about feelings. People don't tend to swim upstream when searching for community. Why should they? If a platform demonstrates over and over that it lacks both the will and means to protect marginalized communities from personal and private abuse, then its demographics will remain significantly white and male, and they will set the tone for what is normal and permissible rather than the people who are at risk.
Choosing to favor no one is not a choice that's available to us, because it's effectively choosing the most exclusionary voice.