the thing is that Europe's history is full of warfare and prejudice that carries on to this day, it's not that exceptional even though Slavic areas have went through a lot of crap. That's got absolutely nothing to do with the criteria of whether someone's white or not white.
I just honestly think that people who see "white" or "poc" or whatever as some club where people get along simply because they belong to the same wide racial bracket are people who've spent a bit too much reading US discussions with the mindset of society somehow being divided into privileged whites who are all part of the same group, and "other" - and if you don't feel like you're part of the same white club obv you must be something else.
White is a pretty wide term. White people from scotland or norway are quite different from white people from southern france or spain or such. There's a lot of variation and it's a bit stupid to legit try to claim that ooh my people are not white because some centuries ago there were some Turkish intermingling in the southern parts and besides we don't get along with the UK right now.
Like Mid-Russian with clear Mongolian influence and such, I can believe is starting to be on the border between white and asian, but Slavic, nah. It's just hysterical nitpicking, like ooh there's some DNA mixed in we're not pure celts we can't be white. for real.