I grew up in a good community in the US, and never really knew any racism. Experiencing real racism for the first time after I moved away is still one of the most painful experiences in my life.
Imagine that you're out celebrating a national holiday with friends and family, happy and content, except that around you there are hundreds of people screaming and jeering that independence day is for Americans, and you should go home. But you are home. You were born within this state even, just up this same river you're all sharing together right now. This is a real thing I experienced in parts of rural America.
You can call me oversensitive to racism, and I'd agree that I can be hyperaware of it. But it's a response to the deep trauma that even just a few experiences with racism has caused me. I just want to live peacefully in the country I was born, but that's not possible if the people around me hate my very presence in their midst.