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.
I think it’s as simple as this: people need an enemy, some person or group they feel is against them. Conservatives get off on having a victim complex, and will straight up make shit up against their opposition just to make themselves look like a helpless little child. “Oh no, what am I gonna do? Me or my granddaughter needs a job and I heard in the news they’re all being taken up by immigrants” meanwhile, the same person is being fed this information from the comfort of their couch.
“The immigrants are taking our jobs” is a sentiment that I have seen at least in my part of the country go down in the last several years and im in a very conservative area. Simple fact is immigrant workers work cheaper and faster than others and they often do better work, people are realizing that.