> Why can't one just peacefully integrate the best they can and accept their differences?
Their complaint is that they want to integrate entirely and can not. They do not want to be different, they want to be the same. They want their kids to be treated the same. And the claim is, regardless of how well you integrate, how well you speak you will not be fully integrated.
I don't know why this mentality pervades the West - the mentality that as an immigrant you are entitled to be accepted by natives. Just because you speak the language and have stuck around for a while, doesn't make you one of them. There will always be irreconcilable differences.
FWIW I will be moving to Japan next year. I don't care if the Japanese 'accept' me. I don't expect to be treated the same, I know that they're somewhat xenophobic, and some of that might be for good reason. I fully accept that I will be a guest in their country. My goal is to do my best to minimise inconvenience to others and prioritise their cultural norms over mine.