A student can spend four years at many colleges and universities and graduate with no real awareness of any other viewpoints than those on the left.
College and university faculties do not simply happen to be leftist. Too often ideological questions are asked at faculty job interviews and ideological litmus tests are applied in hiring.
One reason for the prominence of conservative think tanks is that so many top scholars who are not leftists do not find a home in academia and go to work for think tanks instead.
Not even visiting speakers with a conservative viewpoint are tolerated on many campuses. It seems incredible that there would be fears that a one-hour lecture would undo years of indoctrination. But perhaps it is just sheer intolerance that creates hostility to anyone expressing ideas contrary to the prevailing notions of the left.
Students often report that their professors react against them for stating a viewpoint different from the prevailing orthodoxy of the left. They can be ridiculed in class discussions or given low grades on exams.
Dartmouth College has been carrying on a running battle with the conservative student newspaper, the Dartmouth Review, from the moment it was founded many years ago. On some campuses, conservative student newspapers are destroyed by leftist students or even burned publicly, with little or no effort by the college administration to maintain freedom of speech.
A student at Lewis College in Colorado was actually kicked by a professor for wearing a sweatshirt proclaiming his Republican views. This happened at a birthday party, of all places, and the professor has been quoted as saying that her only regret was that her kick was not "harder and higher."
The American Council of Trustees and Alumni, which monitors campus intolerance, is trying to get some action taken against that professor. Good luck.