It's called "outgroup homogeneity," when you are part of an us-vs-them scenario your "us" always seems to be a coalition of diverse viewpoints whereas your "them" is a single collective viewpoint.
So for example if you are in a team of white males you might want to get a token black person or a token woman on your team to "bring the black perspective" or "bring the female perspective" to whatever you're working on: that's a systematic bias, you're implicitly assuming that there's not going to be a diversity of black/female perspectives the way that you already know there's a lot of white male perspectives.
In fact the broader issue that will lead the US inexorably to civil war even if present communications difficulties abate is that we do elections by dividing our electoral bodies into independent seats and then run first-past-the-post elections for each seat. The issue is fixed-point theorems. Each election is a polity -> polity map; the fixed point of split-FPTP-elections is a polity which is 50% one party, 50% the other party, both parties are completely spineless chameleons which shift however they need to in order to maintain the 50/50 status quo, and people are loosely affiliated with one party while disgusted by the opposition. As the first US civil war showed, this disgust will naturally build without bound until the highly prominent issues at the time cause movements toward secession which then lead to active conflict.
I was going to say "if you're coming from a place that does proportional elections this probably seems like nonsense to you," but that is my own outgroup homogeneity effect rearing its ugly head again! The truth is that even proportionate systems have problems with this sort of divisiveness; witness Brexit in the UK and Geert Wilders in the Netherlands for two examples. But I would insist that there is a characteristic spinelessness that pushes this further from just "we are one nation with serious divisions to reconcile" to "they are awful and we will never reconcile, let's just get a divorce" in the US system.