I certainly agree with you that, on the whole, the US is a far more tolerant country than many of us give it credit for. However, the US was pretty late to the game to abolishing slavery; and it only did so after being dragged kicking and screaming [0]. The south then did everything in its power to resurrect de-facto slavery. And that is just the anti-black racism.

[0] Even the North didn't support abolishing slavery until after the Civil war started, at which point the argument was largely 'we just fought and won a war over this, lets at least get something out of it".