yukonjack has captured my basic thought below.
How many or what percentage are stating a viewpoint? I'd expect most are taking a stance that is consistent with their personal view of the issues of the day. The question really is whether that viewpoint is part of course material or even part of the area of study. If it's really not part of the area of study, then the professor's viewpoint is not germane and can only serve to bias his/her approach to student evaluation. If the course material and area of study actually covers a controversial subject where the professor states a position, I think it should be done in order to generate student interest and discussion that deepens their knowledge of the subject area. The professor's legitimate academic evaluation is then a measurement of the student's ability to conduct academic research that allows the student to state a position that can be supported with evidence and rhetorical skill, not to judge the student against the professor's position with a criteria of right v. wrong.
In my undergrad and graduate studies, I only encountered an absolutely intransigent professor that affected my grade once during undergrad. In my graduate studies, the professors were universally liberal but since I was no longer a callow youth, I was better equipped to stand for my views. I found that my grade was not affected in the least. To keep it in context, the undergrad years were the 1970s and graduate school was early 2000s. I think the academic world has only become much more polarized in the intervening years with adverse effects for students that don't appear to align their views accordingly.
As to the status of the professors in the lawsuit and their approach, I can't say. Perhaps if their names are stated, the RateMyProfessors website could provide some info on how they manage their classroom and grades.
I had the similar experiences in college. I finished grad school in the early 80's and had no issues with my peofessors (including a class in Marxist Economics). But my daughter and son have had the opposite experiences in high school, college and (daughter's) grad work.