Back in the 1980s, my criticism of diversity was that it abolished culture, caused internal conflict, and then genetically erased the population through admixture. After all, this was the pattern we saw happen in ancient Greece and Rome.
Italians today — they were once a Nordic population — have more in common with Persians and Arabs than they do with northern Europe. Greeks today look Turkish more than anything else. And then there is what happened to Spain with the Moors, and Eastern Europe with Asians.
Once your society becomes racially-mixed, you lose the framework of traits that made your people what they were. These are replaced at random in bits and pieces, which means that the collections of traits that make up abilities and inclinations are broken.
If you want to know the future of the West if it does not end diversity through total remigration, it is gradual genetic assimilation by foreigners. We will remain mostly what we are, but with new stuff in, and so we will not think or act the same way.
We will also never rise again. The power of the original having gone, the hybrids will create a society of less potential. It is like being Brazil: ancient buildings, old traditions no longer understood, and a vast sea of mixed-race people who add nothing except doing simple jobs.
When considering the threat of diversity, it makes sense to include the genocide aspect. If you get hybridized, the original group is gone; it has been genocided.
Diversity erases culture, pits groups against each other, deletes social trust, and eventually, simply kills you off entirely through admixture.