I've had about an equal number of really good Leftist and Rightist teachers. All had their quirks, I never agreed with any of them, and I remember most of them fondly.

I've also had about an equal number of really *lousy* Leftist and Rightist teachers. I can't remember the difference between any of them, and all I really remember about their classes was a combined feeling of insult and frustration.

I've also had about an equal number of teachers who were good at teaching their subjects, so long as you didn't didn't get them started about whatever their personal agenda was. There was an economics teacher at my college who was really a good economics teacher, but was at the same time a ridiculously cartoonish fundie, who actually told a graduating class at a commencement ceremony that he would pray to "protect them from the forces of darkness." If you could avoid triggering the fundie switch he was a great teacher... if you couldn't then you just wanted to hide.

An incompetent boob is an incompetent boob, regardless of what he or she believes, and the same goes for people who are good at what they do.