I had some ridiculously militant liberals in my gen eds, but after clashing with them a couple of times, I'd just sit in the back of class, ignore them & ace the class anyway.
The most liberal professor I've ever had, ironically enough, was my Philosophy of Law professor this past semester. He was a nationalized citizen from England who believed that the Consitution (or rather, the Bill of Rights) was counter productive in a democracy/republic & should be done away with because I unnecessarily hampered the populace's ability to make up their own minds on the subject.
The really cool thing was that he was 100% up front & honest about this from day one and said he was telling us, not because he was trying to influence our minds one way or the other, but so that we could be aware of his biases when he was lecturing & take them with a grain of salt. I wrote my final paper & did my final exams on the death penalty & textual extensionalism and ripped into intensionalism (his method of constitutional interpretation), and I got an A in his class. he was the most open-minded liberal I've ever met in my life & I really enjoyed his class.