I think the distinction between racism and xenophobia is quite important.   One way and another a degree of xenophobia - fear of, or suspicion towards outsiders - is something that crops up in all kinds of times and places, and it's probably true to see it as natural enough.

Racism is something else. The focus for racists isn't strangers and outsiders, it's liable to be neighbours picked out on the basis of some insignificant physical difference, who may well be essentially indistingishable in other ways. It's based on a perverted pseudo-science, and on manipulation. There is nothing natural about it.