Last month, 18 million college students returned to school to those hotbeds of debate about the crucial issues of the day, right? But not so fast.

A major new study on the campus climate for viewpoint diversity surveying 24,000 U.S. students and published by the American Association of University Professors found otherwise.

Only a third of college students felt that their professors made learning about different views a priority.

In fact, most did not think it entirely safe to hold unpopular opinions on campus.  Since more seniors felt this way than freshmen, it appears that the college experience makes students less comfortable about exploring and voicing diverse opinions.

This lack of intellectual diversity at our nation’s colleges and universities should be a concern to all of us.

It means that our future leaders in industry, government and science are receiving a one-sided education (at an average cost of $75,000 to $155,000 for a degree) that leaves them ill-equipped, as the report explains, to work “across differences to tackle challenges and create solutions.”

It also limits the phenomena studied, questions asked and solutions proposed by professors who, as the main producers of research and development in this country, fuel our innovative edge.

Why are our colleges and universities such unimaginative places?

As Robert Maranto, Frank Hess and I document in our book, “The Politically Correct University: Problems, Scope, and Reforms,” rather than being a marketplace of political ideas, intellectual diversity is what schools value least.

Instead, it is only diversity of race, ethnicity, gender and sexual orientation all of which are very desirable, to be sure that rules the day in higher education.

This agenda dominates higher education in faculty hiring, student admissions, curricula, student life programs and virtually every other aspect of college life.

Universities assume that (1) demographic diversity has educational benefits, and (2) that we must give preference to race, ethnicity and gender because they are central to students’ worldview and self-identity.

Yet, whether demographic diversity enhances learning is still debated among social scientists.

Intellectual diversity clearly does so, however. As we discuss in our book, studies show that students respond better to multiple ideological perspectives, which stimulates critical thinking and creativity, improves understanding and decision-making quality, and facilitates moral development.

Our sociopolitical values are fundamental to who we are as individuals. It should not be surprising that conservative students feel alienated when their perspectives are excluded from the classroom.

A 2009 study by professors Matthew Woessner and April Kelly-Woessner found that conservative students lack academic role models, have more distant relationships with their professors and have fewer opportunities to do research with professors (particularly on sociopolitical issues).

Such factors may partly explain why there are so few conservative professors. Conservatives and libertarians are becoming increasingly rare in academia, outnumbered by liberals by 3-to-1 even in fields known to be relatively conservative, such as economics, by more than 5-to-1 in moderate fields such as political science and by 20-to-1 or more in many fields, such as sociology and anthropology.

Studies of professors’ party affiliations and self-reported political views show that, on average, liberal professors outnumber conservatives and libertarians by about 8-to-1, with the imbalance being much greater at elite institutions.

So what is the solution? For the same reasons colleges and universities are sensitive to race, ethnicity, gender and sexual orientation, they should include and respect a range of political ideas.

In upholding affirmative action in student admissions, the Supreme Court said in its 2003 Grutter decision that diversity policies are legally justified because of the educational benefits they produce. If so, then schools should include conservatives and libertarians in faculty hiring and admissions.

If, instead, diversity is defined to include every kind of differentness except different political ideas, then our universities will never be truly diverse in the way that matters most for learning and the development of innovative solutions to our nation’s problems.

• RICHARD REDDING