Because approximately 0.5s after you create a whites-only group, you will be savagely attacked as the world's biggest racist. And that's actually fine... but only as long as that is the case for everyone. It's not ok to have self-segregation allowed for some groups, but not others, which is where we are today.

???

Genuine question here, not trying to anger anyone.

But we have Heaven only knows how many whites-only groups online. (In fact we have Heaven only knows how many Asian, Black, Native, and Latin groups online as well.) If you don't like them, you're free to ignore them. Or you're free to criticize them. Your choice. All of that is the great thing about the internet.

Why would any of that be a problem for anyone?