I am not being cute, I am seriously asking. You have to have some sort of criteria to meet these terms. If you don't then why wouldn't every student who did poorly on a paper just complain the professor didn't like their views?
I don't disagree, but I don't think this is nearly as common as you guys think. I mean when were you in college? How would you, or anyone, possibly know what is going on in college campuses around the country everyday? Are there some professors that do that? Probably, but I don't think it is the norm. I think most professors just want you to be capable of supporting your positions, and I think you probably get some students who didn't do well because of their own effort, who like to blame it on their professors.