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"White nationalists" are really just "supremacists" attempting (unsuccessfully) to avoid the negative implications.
Oppression of "non-whites" is implied by their stated objectives since it is the only realistic way to achieve them.
The pertinent fact is that immigrants are here now --- this is not just history or tradition, it is current reality.
Genocide would be an amoral effort to alter this existing reality and enforce "white nationalism" --- by those who obviously think skin color makes them "superior" in some way and grants them to right to oppress or even kill "other" immigrants.
Attempting to justify this by past genocide is an "appeal to tradition".
What about white flight and gentrification? As far as I'm aware, there are extensive legal and governmental measures in place in the US (such as placing low-income housing deliberately to decrease homogeneity [1]) to prevent people from ethnically self-sorting.