Thing is, I have takrn a class like that. Was a political science class. Extreme hard right (chinese dissident, hard anti-left).

I wrote the requisite papers. All of them were F, with no commentary. I brought this to the department chair, and the grades changed to b's and a-'s.

He was absolutely grading on political position for the paper, and not a proper discussion of content per the rubric.

And, aside from going to the chair every time, theres little you can do to fight this sort of obvious bias.