I agree with this.
Can native people really be blamed for this seemingly-normal and natural reaction, though?
I grew up in a very white, very British part of the UK. In my school year there was a Nepalese, a Sri Lankan, an Indian, an Israeli, and two mixed blacks with white fathers. Because there weren't sufficient numbers to form cliques, they were very much integrated. People occasionally teased them with the odd comment, but it was all taken in good humour and they were no more or less liked than anyone else (apart from one of the black kids who took to selling cannabis and randomly assaulting people in the street).
The only person who ever received any racial abuse was an Arab who briefly attended the school, and that was only because he was an arrogant halfwit who insisted on telling everyone how much greater Saudi Arabia and Islam were than the Christian pigs of England.
A lot of people from my town went away to universities in much more 'multicultural' major cities, and received a big culture shock. Some were Enriched© with sexual assaults, others with random attacks amounting to ABH or GBH (including myself), at least one lost computer equipment worth thousands of pounds after a pack of Vibrant & Diverse Melanin-Rich Youths™ broke into his flat.
The word 'nation' has always meant a people with a common ethnic or religious/ideological origin, but now appears to have a definition closer to that of a tax office. Left and right-wing people alike chant the same mantra - why oppose immigrants who work hard and pay taxes? They're not doing any harm, surely?
Bollocks to society, they come, they work hard, they pay taxes
Bollocks to society, they come, they work hard, they pay taxes
Bollocks to society, they come, they work hard, they pay taxes
All well and good until you find, in a few short years, that your town is now 20% black, or Muslim, or Polish.
There's all sorts of factors, aren't there? Are they competing for a job with locals? Are they willing to work for less pay and therefore "native" wages go down or stagnate or they lose jobs? If those things are true, of course it's natural for people to resent it.
In America, the people who are often the most pro-immigration are professional and other high salaried people. The Mexicans or Central Americans coming across the border are usually very un-skilled or semi-skilled people, and so they're no threat to American elites. It's different for American factory workers, or landscapers, or gas station attendants.
If, like new groups of any variety or race they find it hard to make a living because of poor skill sets or language skills or lack of contacts, and so a percentage of them turn to crime to make a living, the resentment is even worse.
Then, what if they don't try to assimilate? It's one thing if it's a person here or there, who is, in effect, forced to assimilate, which, btw, is what happened to our family, but, as you say, what if it's a really big group, which, as is often the case in these situations, creates their own area or part of the city, where you are no longer comfortable shopping or using social amenities because they're all speaking a "foreign" language, the food is strange, they seem very clannish, etc. You can wind up feeling like a foreigner in your own country.
I'll be honest, I've found it upsetting in a few situations even here in the U.S., which is very multi-cultural. The Chinese, Koreans, etc. are often lionized as "model" minorities, and yes, it's true that they commit very few crimes, are very hard working, and push, sometimes maniacally, for education for their children. However, when there are large numbers of them going to one city, they create virtually homogeneous cities of their own, can be very clannish, and have trouble assimilating to the mores of the people around them. I used to think that once the children were gone I might move west again into what we call the borough of Queens, part of New York City, where they have very nice condominium apartments in high rise buildings, right on the water with beautiful views, with maintenance staff to take care of everything, markets, shops, gyms and theaters right downstairs. After a lifetime of what seemed like unending taking care of a house and property and driving constantly, it seemed like an attractive option. I went to look at some a year ago. In the space of five years there had been a huge turnover in the area. Every single person in those high rises was East Asian. You couldn't hear one word of English. I couldn't even read the signs on the stores. There's no way I would be comfortable there.
It's even more discomfiting when I see things like that in Italy, no matter the origin of the immigrants, because it's just not been part of the Italian experience, and what I long to re-experience.
So, yes, I think it's normal. People differ in their level of comfort with those sorts of quick, drastic changes in their "world". That doesn't mean there should be any tolerance for violence or maltreatment of foreigners, of course.
The question is, how do you solve this problem of self-enclosed, large, minority "ethnic blocks"? Denmark said recently they want to end the practice of migrants living in these homogeneous, non-assimilating blocks. How do you do that, though, in a free society? If people want to buy an apartment or house near people from the same background, how can you prevent them?
If you need foreign workers, and let in large numbers of them, or the borders are too porous, or you let in more refugees than you can absorb, and the people involved don't assimilate, these are the issues that arise.
I certainly don't believe that there should be no borders between countries, as the Democratic Party in the U.S. now seems to be saying.
What has surprised me in terms of the Poles in England, however, is that the British people I've heard speaking about the issue on the BBC or chat shows seem more upset with the Poles and other Eastern Europeans than with the Caribbean blacks or whatever. Is it the language issue? They don't want to hear foreign languages in the street or the shops? Is it that there's more competition with Poles for jobs? Are some groups off limits for criticism, so they take it out on the ones who aren't "protected"? I don't know. It would seem it should be across the board if they're going to be resentful.