The US is a nation plagued by white supremacy. Seems like a reasonable position to hold. They aren't celebrating the destruction of whites but instead the destruction of white supremacy. Through race mixing, being "white" is going to become a rarity within a dozen more generations and, if we don't obliterate ourselves by that point, completely nonexistent afterwards. It is difficult to advocate the propagation of a white majority without being racist. It explicitly requires cutting oneself off from those icky brown people.
It's challenging to fly the white power flag if you aren't white, and it's not morally or ethically questionable when you became not-white through loving and starting families with those aforementioned icky brown people. A reduction in white people is a natural effect of open intimacy with other ethnic groups. It's not a deliberate attack nor is it a racist agenda. The more accepting white people are of others, the less white people there will be in the future. This is what happens when skin colour is an easily altered component of genetic human physical characteristics.
Of course, then you've got cosmic-brained people who don their I-am-very-smart hats (MAGA, or your white-wonderland European equivalent) who are very genuine in their concern that more icky brown people will dismantle their crime-free, prosperous utopia. It's a serious concern, you see. The statistics!