Why do some people in the USA assume all immigrants are illegal and should "go back to where they came from"? Shouldn't that logic apply to all non-Native Americans?
Not everyone thinks this, but I know an extreme right-winger who thinks this. He is also a conspiracy theorist who thinks non-white people are out to get white people so, yeah, odd.
Not every immigrant is illegal or bad. I know a girl who didn't speak English for 3 years when her family legally immigrated, so of course she's been told this.
It's inherent feature of human reasoning across the board. Everyone does broad generalizations about other people based on more or less unrelated information about them. Just yesterday someone here was getting upvoted for implying people driving lifted trucks are racists. It's the same logic at work there. It's othering. Us vs. them and so on. It may have been useful when we still lived in tribes but doesn't quite work with how society is today.