I suppose we all have a tendency to believe things that support our worldview, but this worldview is, you know, wrong.
I think it's perfectly fine for people to want to shut down immigration to the US. I don't agree, but it is a valid policy choice (though abusing the hell out of human beings in pursuit of that policy choice is a different story). I don't doubt that racism is generally a big part of that desired choice, but it still is the kind of policy choice which elected governments are supposed to decide. The weird fantasies people have about scary brown people are pathological. Immigrants just aren't rampaging across the country raping all the good white women and shooting all the good white men. Why do people want to believe that?