The "rude or abusive" flag links to the Code of Conduct.
Regarding this specific answer, this section is relevant:
We don’t tolerate any language likely to offend or alienate people based on race, gender, sexual orientation, or religion — and those are just a few examples. When in doubt, just don’t.
The answer in question alludes to the white supremacist idea of a so-called white genocide and pushes lies about supposed calls to "abolish Whiteness" or calls for a "genocide of Whites". It white-washes white supremacism by falsely stating that it is "simply [about the] survival of [the] White race". It uses white supremacist code words like "anti-White discrimination" and "racial awareness".
The answer promotes this "racial awareness" to "fight to survive" against a "white genocide" braught about by "destructive ideologies". This sort of white supremacism certainly is "likely to offend or alienate people" based on the categories listed in the CoC.
For context, the user in question is a white supremacist who in other answers said that Jews control finance, media, academia, politics, etc and promote third world immigration, abortion, feminism, homosexual agenda, etc. The answer in question is along the same lines, just with a bit more dogwhistles thrown in.