For those who require proof, evidence for predominantly left-leaning university faculties keeps accumulating. The interesting part is the denial.
John Tierney's "Why Righties Can't Teach" sheds some light. He notes that, "[s]ocial scientists call it the false consensus effect: a group's conviction that its opinions are the norm. Liberals on campus have become so used to hearing their opinions reinforced that they have a hard time imagining there are intelligent people with different views, either on campus or in politics."
These, of course, are the diversity champions.
Some of us are fortunate because we somehow got in under the radar. My students grasp my various biases and most also accept the idea that there are few pure and unvarnished sources. Rather it is each individual's responsibility to compare arguments and process them.
This is the opportunity that we deny students when professors parrot party lines -- and when they succumb to the false consensus effect.