A person who is half white is not a white person, that is a half-white person. If someone is 99% white and 1% something else, okay, I will call that person white. 50% is too much to ignore though. If you mix 50% red paint and 50% blue paint, you do not have red paint, nor blue paint. You have purple paint. It is something different.

And it's not a matter of 'half' either, it's a matter of less since we are facing the reality of white people becoming minorities in their own countries. You're the one using the 'one-drop rule' if you think someone who's 1/8th white and 7/8ths something else is a 'white person'. We are 8% of the world's population and declining, and at present immigration and birthrate trends we are set to become nothing more than a small amount of admixture in a foreign population. The modern human is ~2% Neanderthal genetically. You can't tell me with a straight face that Neanderthals aren't extinct, though.

Genocide through forced assimilation, without murder, is still considered genocide by the 1948 UN Genocide Convention and has been noted as genocide by human rights scholars in various occurrences.

https://www.humanrightsresearch.org/post/genocide-and-its-denial-the-power-complexity-and-limits-of-a-contested-concept