It's weird when I think about it, because colleges and universities we're created with the essential purpose of promoting and instilling critical thinking to their students. The students, in turn, must apply their understanding of critical thinking into many aspects of their education and, possibly, their personal beliefs. The whole idea of promoting a diversity of opinions and ideas is almost counter-intuitive to that aspect.
Colleges and universities with an ounce of credibility do not invite creationists or anti-evolutionists to deliver speeches on their campus. Why? Because they are anti-science. The same thing applies to climate change deniers, especially those with ties to corporations and lobbyists that are promoting anti-climate change. Those people, I reckon, are not there to promote critical thinking if all they're going to do is push a biased political agenda that runs counter-intuitive to what the college or university promotes.
With the probable exception of economics, politics can't really be completely measured or quantified through the scientific method alone. Nevertheless, a base line has to be set over what kind of politics a college or university is willing to tolerate. Ideologies like pure socialism, communism, totalitarianism, monarchies, oligarchies, and even anarchy are still taught and discussed even if most professors and university execs don't believe in them. If a professor personally has a libertarian-left ideology, it does not prevent him from promoting and debating conservative ideology.