"White" as is used by many white supremacists is not a race. It's an ideal figure that you're supposed to look up to and wish to be like it, and just like gods or supermodels it's not meant to be real or even attainable since that's not the point.
What's important is to focus on all it's virtues and never acknowledge it might have any kind of defect.
From here comes the natural explanation as to why you're told that just about anyone ever isn't white. Because people aren't perfect and everyone has problems or defects of their own therefore nobody can be the mythical "white" that you hear so many claim that they are.
However, as long as the ideal stands, some people can be easily goaded into not inly worshipping it but even believe themselves to be "white" as well since being equal to that ideal means there's nothing wrong with you. It's easy to understand why so many edgy teenagers with no direction in life or societie's fuckups that have no idea what they are doing with their life would jump at the oportunity of being an awesome person, responsible for the craddle of all civilization and culture and with no defects, especially when there's no work involved, you're "white" by default according to your skin color, right?
In truth, the excessive focus on race is ridiculous. There are genetic differences between different races, of course. But that doesn't necessarily mean they are inferior. See Africans and their genetic resistance to malaria and other diseases for instance.
I'd argue instead that the culture of a nation ends up being far more important than even their race as that's what shapes their minds and what they do.
Therefore the idea of a "white race" is ridiculous, but a "white culture" is a far better one for everyone.
However there's a problem with "white culture" that makes very little people actually care about it, even "white nationalists".
It takes work and passion.
White culture is about excelling and mastering something, especially if you are passionate about it, all for the sake of evolving or simply to do better than the previous generation.
Our great artists didn't just made their art because they were paid to, they did so because they wanted to excell in their areas and be better than the previous artists.
Our scientists and engineers did not create so many things because they were paid to, they did so because they wanted to make the world a better place than it was the day before, because they wanted to do better than their ancestors.
This kind of drive is not found in many other cultures and our evolution is proof of that. However if you hear "white nationalists", you'll get the idea that this is inherent to you for being white and yet there's plenty of NEET's and other social fuck ups that will gladly waste way inside their house never mastering anything except mastubation. But it's easier and more appealing to them to develop a sense of superiority due to their skin color than to actually go out and do something with their lives.
You want a simpler example, think about ghetto and thug culture. We associate that with niggers in the hoods and thus claim that niggers are all criminals. The reality is that ghetto and thug culture breeds criminals, not their skin color, to the point that even white people born in those conditions end up as thugs as well, while black people outside of that culture and preferably in a "white culture", end up being far nicer people.
The only thing you actually have to worry isn't race but rather idiots dilluting culture and mixing a superior one with crappy low effort ones. Of course, the race supremacists don't help much here, all they do is fuel the other side instead of letting the free market ruin the idiots that refuse white culture.