The presumption here is that "America is not a racist country" is a racist statement on its own. Nobody is claiming it is. The problem arises in what that statement does for the racists in America; it legitimizes their behavior, which means it supports people and actions that do suggest one racial group is inferior or superior to another. It's that knock-on effect one ought to think of as fitting the definition of "racist", not the idea itself.

Also why do so many people absolutely lose their minds when they find out that tribalism is a human trait, and when applied to racial groups, results in racism? I really don't understand why the idea that everyone has racist impulses causes such despair for some specific set of people.

The problem isn't that you're a human being, the problem is refusing to try to do better than your base impulses.

"Racist" isn't a brand. It's a neon sign you flip on and off 300x a day, depending on what you do and say.