@RW Standing,
Your remarks assume that "cultural and racial diversity" are laudable and to be strived for. The likely outcome of several more generations of intermarriage and cultural diffusion in a technologically sophisticated milieu will be that racial distinctions will no longer exist, and that cultural distinctions will be largely relegated to fields of entertainment or of scholarly inquiry. The Danes invaded England in the ninth century, and, despite their best efforts, failed in every attempt to obliterate the Saxons. Eventually, Canute of Denmark landed in Wessex, and after more than a year, succeeded in conquering England. He lasted for fewer than 20 years thereafter, and neither the English language nor Saxon culture perished during his reign. A little more than 30 years later, William the Bastard of Normandy successfully invaded and overran England, and no Saxon monarchy would ever rule there again.
But so what? The English language was enriched by its exposure to French, but in the end, the language of England remained English, and French faded away as an everyday language there. Culture certainly changed, and in many respects (governance, feudal relationships, commerce) it changed radically. I can see no good reason to condemn those cultural changes, as their eventual effect was to the benefit of the nation.
Should we mourn the lost post-Roman culture of the Britons? The Britons are still with us. Should we mourn the lost culture of the Anglo-Saxons? The Anglo-Saxons are still with us.
I think you protest too much. Very likely 'racial" intermarriage will obviate the one objection, and in the case of culture, the historical evidence, at least, is that culture is neither static nor worth eternally preserving.