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.
For some reason it seems like human nature to treat everybody in a recognizable group like they’re the same person, and that person is either good or bad depending on your background and attitudes - immigrants, trans people, cops, boomers, tech nerds, hot women, republicans, democrats, musicians… there are probably stereotypes you have broad opinions about which you will spend all day defending/rationalizing because a) “it’s true” and/or b) “I’m not bigoted!” We’re all bigots, just do it in different ways. And no, that’s not a defense for any particular bigotry or saying they’re all equal.