David French is the president of the Foundation for Individual Rights in Education, a nonpartisan group that monitors free speech on campus. In a 2005 interview with ABC News , French argued that "the universities have been so captured by the left point of view, that you're going to get more political and intellectual diversity at your average suburban mega-church than you are at an elite university." The cause, he believed, was the systematic suppression and censorship of conservatives.
That same year, Rothman, Nevitte and Lichter published a paper  using data based on a telephone survey in 1999 of approximately 4000 faculty, administrators, and students. The purpose of this study was to test if professional advancement is influenced by ideological orientation. What they found out, was that conservatives and Republicans taught at lower quality schools, compared with liberals and Democrats. This suggested, they argued, "that conservative complaints of the presence and effects
of liberal homogeneity in academia deserve to be taken seriously".
A 2014 study by Iyengar and Westwood  underscored how powerful political bias can be. In an experiment, Democrats and Republicans were asked to choose a scholarship winner from among fictitious finalists, with the experiment tweaked so that applicants sometimes included the president of the Democratic or Republican club. Four-fifths of Democrats and Republicans alike chose a student of their own party to win a scholarship, and discrimination against people of the other party was much greater than discrimination based on race.
For a 2016 study , Shields and Dunn surveyed 153 conservative professors. “As two conservative professors,” they wrote in The Washington Post, “we agree that right-wing faculty members and ideas are not always treated fairly on college campuses. But we also know that right-wing hand-wringing about higher education is overblown.” Nevertheless, about one-third of the professors professors admit to using "coping strategies that gays and lesbians have used in the military and other inhospitable work environments", ie they "closeted" themselves by passing as liberals. Some also said they were badly mistreated on account of their politics.
In a 2017 speech before the Stanford Board of Trustees , former Provost John Etchemendy argued that he "watched a growing intolerance", "a political one-sidedness, that is the antithesis of what universities should stand for". "It manifests itself", he argued "in the intellectual monocultures that have taken over certain disciplines; in the demands to disinvite speakers and outlaw groups whose views we find offensive; in constant calls for the university itself to take political stands".
In 2009, world–renowned political scientist Norman Finkelstein was denied tenure at DePaul University for his criticisms of Israel's human rights violations against the Palestinian people . In 2014, co-discoverer or DNA James Watson was forced to sell his Nobel prize after losing most of his income for stating that people of African descent are less intelligent than white people . In 2017, graduate student Lindsay Shepherd was hauled before a three-person panel at Wilfrid Laurier University, which interrogated her for more than 40 minutes for showing a first-year communications class a video snippet from TV Ontario of Jordan Peterson debating another professor on the use of gender pronouns . In 2018, University of Pennsylvania Law School professor Amy Wax was removed from teaching mandatory first-year courses for saying in an interview that she didn't think she'd ever seen a black student graduate in the top quarter of the class .
These are some of many examples where academics / scholars have been reprimanded for making statements deemed too "politically incorrect" by their employers. While such cases are obviously but annectodal evidence at best, they do suggest Etchemendy may have had a point when he said he watched a growing intolerance "that is the antithesis of what universities should stand for". They do suggest it may indeed be safer for conservative professors to pass as liberals. They do suggest that French may have had a point when he argued there was systematic suppression and censorship of conservatives. And they do suggest that Rothman, Nevitte and Lichter may have been right to conclude that that conservative complaints of the presence and effects of liberal homogeneity in academia deserve to be taken seriously.
 Pierce, Fort (2005) "Conservatives Censored on College Campuses?"
 Rothman, Stanley; Lichter, S. Robert; Nevitte, Neil (2005). "Politics and Professional Advancement Among College Faculty"
: Iyengar, Shanto; Westwood, Sean (2014). "Fear and Loathing across Party Lines: New Evidence on Group Polarization"
 Jon A. Shields; Joshua M. Dunn Sr. (2016). "Passing on the Right: Conservative Professors in the Progressive University"
: Etchemendy, John (2017) "The threat from within"
: Klein, David (2009) "Why Is Norman Finkelstein Not Allowed to Teach?"
 Perry, Keith (2014) "James Watson selling Nobel prize 'because no-one wants to admit I exist"
: Walkom, Thomas (2017) "The problematic case of the Wilfrid Laurier TA who dared to air a debate on grammar"
: Diaz, Andrea (2018) "Law prof ousted from first-year classes after saying black students never graduated top of their class"