There are many Europeans I share genealogical origins with that I would vehemently oppose and lack social cohesion with, just as I am sure there are many Mexicans whom I share no blood with that I would have high social cohesion with. It is not a controversial idea that, as an American, I should desire for those who live here to follow the same laws, standards, and patriotic beliefs me and my neighbors adhere to. If you hate America and wish for its demise, break laws, and refuse to live by the few social norms imposed upon you in America, then I genuinely do not want you here.
By social cohesion they probably mean social cohesion. Assuming the worst creates noise (and is explicitly against HN rules).
The fact that two people from some pairings of cultures don't socially cohere as well generally, on average than two people from the same culture shouldn't be a controversial thought. It's demonstrably a non-negligible issue. I've seen it undeniably harm teams and make everybody basically miserable, first hand, three or four times. Of course if one uses that fact to attempt to spread hatred, then that is a problem.
Why do this curt shitcoating of another person's honest opinion?
Edit: And as a sad disclaimer, I am not defending the parent's person. I do not know them. I am only criticizing your response.