The Left likes to blame the Right. Figures like Donald Trump are said to be 'divisive'. But the current resurgence of rightism, often denounced as 'extreme', is perhaps best interpreted as a reaction against the increasing cultural dominance of leftism. It's a reflection of the fact that leftism has become gradually more intolerant as it has acquired power – suffocatingly so, from many people's point of view.
As with any social phenomenon, the causes of increasing polarisation are complex. But one reason seems to be that for many people, their opinions have taken on (in their own minds) the status of fact. They 'know', for example, that men usually oppress women, that white people are all racist, and that economic inequality is unjust. Opinions that diverge from these 'facts' are simply wrong. They don't deserve to be given space. Rather, they deserve to be suppressed and punished.
Where did people acquire this unjustified certainty, and the inability to consider they might be wrong? I suspect the answer in many cases is, they acquired it at university, at least if they studied a humanities subject. Marxist and Marxist-inspired perspectives, which promote dogmatic ways of thinking, have gradually infiltrated the academic humanities. By now, such perspectives have become dominant in many institutions, including blue-chip ones.
Not all Marxist perspectives are necessarily wrong, so long as one remembers they're just perspectives. The reasons for social stratification (for example) are not well understood; arguably, they're not understood at all. Marx's theory that inequality is due to 'oppression' may be correct, in part, but there's currently no way of knowing. It could be completely false.
Marxist-inspired perspectives on gender, sexuality and ethnicity can be intellectually broadening, if that's considered an objective worth pursuing – so long as they're presented as perspectives, and not as compelling theory, with alternatives or critiques dismissed as 'ideology'. But that doesn't happen in practice, and it's not clear if it's even feasible. It's an integral part of the Marxist approach to treat itself as both factually and morally correct, and to treat other ways of thinking as deluded and harmful. This is one important way in which Marxist analysis is very different from the scientific approach.
Marxism is toxic to the spirit of free enquiry. It regards 'free enquiry' as an instrument of oppression. It's not surprising that support for neutral debate, and dispassionate weighing up of alternatives, has declined, if professors encourage their students to regard such things as merely a cover for dodgy agendas.
Rather than teaching people to think sympathetically about a range of differing viewpoints, many humanities professors encourage adopting faith-like positions on certain topics. They don't do it by stating categorically that (for example) men oppress women; the process is more subtle than that. Students are encouraged to think 'critically', but only in certain directions. Getting good marks depends on getting to the 'right' conclusions, and avoiding the 'wrong' ones.
For example,
• anti capitalism: thumbs up.
• anti state intervention, or anti Marxism: thumbs down.
Ironically – or hypocritically – it's actually the humanities that are doing one thing (political propaganda) under the cover of another (intellectual analysis). It's made to look like science, but has more in common with religion.