Do I Repeat Myself? Very Well Then I Repeat Myself, ...

(I am small, I contain like three ideas. Four tops.).

[With apologies to you-know-who.]

One of the most important facts about the contemporary progressive left is its dogmatism / stifling of disagreement and contrary evidence. 

That's why it has such a powerful tendency to employ indoctrination / brainwashing. It doesn't think that there IS another side of the argument--or, if there is, it's evil. 

Liberalism (in the broad sense that includes most conservatism; i.e. prope-liberalism) emphasizes reason, process, and intellectual autonomy. It uses consensus (including tradition) as touchstones that must be respected for formal / process-y reasons: status quo and consensus tend to get presumption--despite the fact that prope-liberalism is explicitly and enthusiastically committed to the proposition that both are often wrong. Prope-liberalism is committed--in principle, though it often errs in practice--to fully airing opposing arguments. Consensus is a subsidiary goal, in part because agreement among different people/perspectives is taken as one of our better practical signs of justification, ergo of truth. 

The progressive left says fuck all that. Its specific, material goals are its only aims: it seeks the adoption of certain actions, policies and laws--and, of course, beliefs and sentiments. That is: it rejects prop-liberalism's principle of the priority of the right over the good. 

So: giving only one side of the story, stifling disagreement, destroying the lives of opponents, and indoctrination/brainwashing are all fine according to the progressive left. In fact, they're obligatory.

This is the link between the illiberal left and dogmatism/PC. By undervaluing--and even criminalizing--disagreement, progressive leftists become more and more locked into PC orthodoxy.