Not sure about them, but having lived or spent time in a many other cultures and countries, I found that I'd often start off with a cheery or neutral view of them but then when I get to know them and actually live with them there were points of cultural contention that were a lot less tolerable up close than at an easy distance where they were not my concern and that can often show up as projected as "racism." This doesn't mean they do things the wrong thing, it's just annoying to have to pick up a bunch of new and often incompatible new cultural systems to accommodate immigrants. If you're going to them, that's one thing and comes with the territory; but when they're coming to you and maybe you're already exhausted with johnny keeping you up all night and working enough hour to pay rent that extra effort to accommodate 10 extra different cultures 9 of whom might be unhappy if you treat them all the exact same could obviously be exhausting.

Then you start thinking maybe your mental or even physical burden could be lessened if you just had to deal with one cultural system or at least the previous number of ones you had to deal with. You start thinking maybe something like 1000 new Afghans would be a bit harder to deal with for you than 1000 new Frenchman. I don't think there's much stronger way of bringing about racism than actually getting to know and see other cultures, at a distance you can gloss over about anything as "we're all equal humans who should sing koombaya" but the rubber meets the road when your kid is trying to sleep for school and the local arabs have set up blaring calls to prayer at 2am.