Bears repeating.... put that on a bumper sticker; and I'll buy 2.
My daughter was in a French class last semester and the instructor would constantly urge the students to attend various political rallies and protests (all anti war anti Bush of course). The instructor was nice to her, but she was afraid to give her conservative opinion because in the past when she has done this her grade went from high B to low C... A lot of grading is up to the whim of the instructor and it is hard to protest a low grade on a project or essay.
It's not just PC to remain quiet... there is a very subtle threat to your future and livelihood.