Ohhhh you’re not an idiot, you just misunderstand what “uniform” means. “Uniform” means “the same”, with a specific connotation of equality and homegenity. I think you’re looking for the word “intrinsic” - meaning it’s an integral part of something, a base layer. As you said, “fundamental to something’s existence”.

If racism were uniform across the US, it would be equally as bad everywhere, people would be getting beaten and lynched for being Black in Seattle as much as in Birmingham. Which is obviously not the case. But to say racism is intrinsic to the US, I can kind of see that. Racism, as a thing, is built into every layer of the country, though it’s expressed more or less severely in certain areas.

I would rather say racism is endemic in the US, which implies that it could be eradicated, though it would be very difficult to do so.