Kevin, here is a point that must have been missed on you: The professor is the boss of the class! No matter how much you may disagree with the boss, it is best to keep your mouth shut after a certain point. Plus, the professor would almost undoubtedly know more than you about the particular subject of the class since they are teaching it.

Do you really think an employee at Kelly Chevrolet/Hyundai/whatever other foreign car he sells there is really going to walk into his office and say, "Mike, your far right wing economic proposals have already been tried and they have failed. You are a fool for even suggesting them." If those two got into an argument, do you really think Mike Kelly would not hold that against the employee? When it comes down to it, the employer (in your case the professor) is always right in the end, the employee (you as the student in the case) is always wrong. I doubt the professor lowered your grade because of one argument. With your attitude, it was probably a number of things which led up to that point.