Racism comes in many forms, it's not just about being scared of black men on the street. That's a wildly exaggerated strawman.
Everyone has biases and prejudices. Everyone. Yes, that includes you.
But people don't have the same biases and prejudices. People differ in what they're prejudiced against (or for!) and they differ in the magnitude of their prejudice.
And let's be clear: this is not just about skin colour. Gender, sexual orientation, class, accent, formal education... people have prejudices against all of these things and more.
Unconscious bias not a type of prayer or cleansing ritual. You don't stop being biased or prejudiced because you do UB training.
It is supposed to help you identify when and how that prejudice manifests itself so that you can take a step back and try and consciously try and remove your prejudices from your decision-making.
And if you reject racism, why not arm yourself with this tool? If you're not racist (or sexist or classist etc...) Why not take a couple of seconds to think "has some stereotype about this person lead me to this conclusion? No? Okay, let's carry on..."