An example would be a specific part of Bradford, where my parents-in-law grew up and still live. This area has become almost entirely dominated by Muslims during their lifetime. This has been a huge culture shift in their small part of the world. This is not, as far as they are concerned, a wonderfully vibrant multi-ethnic experience. They feel completely at sea and isolated in the area they grew up in. They are angry that this has been allowed to happen.
Areas change all the time though. I used to live in a pleasant, rural market town, that had pretty much everything you needed day-to-day and where a 4x4 was a mud-splattered Land Rover used for lugging hay and stuff around; now I live in somewhere that the affluent Londoners have flocked to, but I'm still in the same place. The useful shops have been replaced by "lifestyle" shops selling overpriced soap, "artisan" bread etc and you can hardly move for Chelsea tractors parked outside overpriced coffee shops.
I spent the first half of my adult life living in a part of South London where the demographic changed dramatically from hugely working-class white to predominantly south Asian Muslim over the course of about 20 years. That was infinitely preferably to the gentrification that is taking place where I live now, at least the locals weren't driven out of their home town by house price inflation, like they are here.
You can't expect the place you live in to stay the same just bea=cause YOU still live there. Culture shifts happen all the time. Look at places like Brixton and Notting Hill: from working class, poor white people, to poor immigrants from the Commonwealth, now the domain of posh nobs and rich hipsters respectively.
It's ok to be pissed off about that sort of change and I get that it's unsettling. Being pissed off because the people moving in to your community are of a different race/nationality/religion is simple prejudice and xenophobia, though, and that's where the rot sets in.
I can remember when racial discrimination was legal. I saw what damage it did and how unfair it was. In my teens, racist graffiti, racial abuse and racial attacks were commonplace and the National Front was very active in the area I lived in. It was awful, sickmaking to witness.
I didn't spend years opposing racism just to see the country I love become dominated by racism and the ilks of Tommy Robinson, Farage et al. And the fact that the rise of the "respectable" right in the form of UKIP and their fellow travellers has created a climate in which it's ok to spout racist shite as long as it's couched in polite language terrifies me.