Well firstly, every society that has ever existed has had a concept of in-groups and out-groups. Frequently based on skin color. Northern European caucasians didn't somehow 'invent' the concept.

But, because 1) I want to get get lunch, and 2) I don't think this is going to be productive, even if they had, somehow created, then metaphorically patented the idea (which they didn't, but whatever) if someone does something to you, is it better or worse to let that go and move forward? Or should you cling to it forever and use it as justification forever after?

You don't need to answer, and while I was hoping to reach some common ground I see that's impossible with you, so I'm done. But you should maybe consider thinking about that for a while.