> How is it that immigrants and especially their kids are a fundamentally unassimilable mass

I didn't say this, but since you are perturbed, I shall address it for you, so that you can understand my own perturbation.

First, I come from the perspective (as a non-American) that the culture of my country, as it existed over the last hundred years or so, has value. It is a culture which proved itself capable of taming a wild land, from pioneers to industrialists to a post-industrial technological civilization. This was a mighty undertaking which cost many lives, all of which were spent in the name of a better future for their descendants. I am the inheritor of such a legacy, having descended from people that made their way West in the 1600s. I have the "privilege" of being the descendant of countless generations of farmers, most of whom did not own their land, going back to time immemorial.

Second, I come from the perspective of someone who is married to a child of immigrants, from a vastly different culture. This gives me a broadened base of understanding, I think, having visited her ancestral homeland several times and seeing the rapid pace of change there as Western ideas and methodologies are picked up, adapted, and even improved upon there. I am not against immigration, I am not against other cultures, and I am not against change in my own nation - within limits.

I would like to introduce the concept of "cultural carrying capacity": the rate at which new people can be introduced into a culture and be effectively absorbed by it. This absorption doesn't have to imply total assimilation; but it does imply the primacy of the host nation's original culture, in the form of its languages, its religions, its values, and its control over the great national project and destiny. This is not to say that such things should be unchanging, but rather to say that if I wish for the stability and continuance of my culture over time, preventing all of this from being deconstructed is a basic necessity.

If a nation brings new people in at a rate below the maximum carrying capacity, it will do fine. This rate is slow enough that new immigrants are able to integrate; they're forced to learn the language, their new friends and coworkers are primary native, and their lifestyle adjusts to be virtually indistinguishable (in public) from the locals. They retain their traditions, language, ritual, religion, etc. within their family and maybe with some fellow immigrants, but by and large they're the same as anyone else. Their friends are a diverse group; their political concerns are based on policies and projections, not group affiliation; their goals and desires can be expanded to include the nation at large, not just their identity group. This is the ideal case.

If you bring people in at a rate higher than the carrying capacity, this effect is diminished or stops altogether. People are able to find insular bubbles of their original population, they can continue to speak their first language, they don't need to adapt to the local area more than is required by law and interaction with institutions. They may form a political block, elect their own representatives, and force institutions to cater to their language and cultural needs.

Is this to the detriment of the locals? It depends on too many variables to name. What is clear, however, is that if you bring your culture with you and set it up here, you will also most likely set up the problems with your culture, as well. The mitigations in place to prevent violence and crime in the local population which have evolved over decades or centuries may not apply or work. Disruption in business, in organized crime, in politics, and within the leadership of institutions becomes the name of the game, never actually decreasing as long as the influx of new cultures is constant.

If we become a nation of people who hail from nations where corrupt politics are and have been the normal state of affairs for centuries, we should not be surprised when our own politics become corrupt. The same goes for whether fathers stay with their families, whether violence is used as a way to settle personal disputes, whether bribery is part of how law enforcement operates, and whether nepotism is the standard mode in business. We all know that there are many countries where all of the above are the normal state of affairs; we also all know that the West somehow threw off much of this, and was engaged in a cultural project of moving away from such venal operations, before the 1965 Hart-Cellar Immigration Act....

One need only look at the countless examples of cities like Minneapolis, formerly a safe midwest city full of White people, now the violent home to the largest number of Somalians outside their home country. It happens slowly, and then all at once... each step of the way lubricated by everyone's unwillingness to say what everyone is secretly thinking. Somehow, along the way, it becomes more beneficial to find ways of hiding the truth by changing the statistical rubric than it is to actually confront the situation at hand.

Now, consider that different cultures have different values around families and reproduction, as well. Immigrant families may have a far higher birth rate than the host population who have stabilized over time, particularly in the West where sex ed and birth control have been mainstays for 3 generations or more now.

If you bring people in at a multiple of the rate of the carrying capacity, as has been suggested (Canada to 100 million people by 2100 is a number serious people are suggesting, for example) the result will be the complete replacement of the host population with a conflagration of new cultures. Some people will do well in this vain, others will not. Some areas may be peaceful, some may be embroiled in total race war, or gang warfare between the fading vestiges of the native organized crime and newcomer gangs. The result is essentially unpredictable and unmanageable.

I have no problem with immigration, friend, but I do want the culture that built my nation to continue to have a strong, permanent presence. I do not want the high-trust culture my ancestors sacrificed to build frittered away so that we can check a diversity box on some form; I do not want to be told my ancestors were evil, and watch their statues be torn down, and watch their legacy be wrecked by someone high on Marxist idealism that knows nothing of what it actually takes to build upward. Yet, those people are more protected by the institutions our ancestors built than I would be if I tried to counter-protest them.

Alas, nobody in power feels this way, even though a massive section of the population does. Democracy has failed us, because it refuses to address this need. The result may be anger that spills over into violence, or it may be a slow and whimpering defeat. I think the latter looks more likely at this stage; the pathological altruism my people are famous for, a game-theoretical advantage in isolation, will be our undoing in the long run.