We are no longer in the realm of a marketplace of ideas and instead are in the blighted heath of blind coercion.

 From Public Affairs by C.P. Snow.  

Snow is the originator of the Two Cultures thesis.  In early 1959 he did a couple of radio programs which then led to his publication The Two Cultures and the Scientific Revolution later that year.  From Wikipedia:

Its thesis was that science and the humanities which represented "the intellectual life of the whole of western society" had become split into "two cultures" and that this division was a major handicap to both in solving the world's problems.

Hardly an exceptionally contentious issue but one which did lead to a lot of debate as to whether there were two cultures, just how distinct they might be and whether indeed there was a divergence between them which had negative consequences.  

The debate continues in many quarters under different guises - EQ versus IQ, emotional thinking versus logical thinking, feeling versus thinking, holistic thinking versus deterministic thinking, etc.  Lots of variations, often riding on small definitional distinctions.

Over time Snow modified his original opinions somewhat and became more precise in his language, but basically remained on the position he had originally carved out.  

But the debates could be heated and prolonged.  Snow was a gifted writer and debater and was open to anyone.  But over time, he began to winnow out individuals who could not be relied upon to argue in good faith.  

With BLM, Antifa, Critical Theory, Postmodernism theory, etc. we are in much the same position.  We accept as a critical position that everyone has a place in the marketplace of ideas, even the most profoundly stupid and or evil ideas such as BLM, Antifa, Critical Theory, Postmodernism theory.  However, when electing whether to debate, we are hostage to whether there is even sufficient common ground to warrant such a debate.  If, as is the case with BLM, Antifa, Critical Theory, Postmodernism theory, there underlying philosophical position is tautologically incapable of such a debate in the marketplace of ideas, then there is no warrant to debate.

It goes against the mindset of the Classical Liberal mind and the values of the Classical Liberal heart, but it is inescapably true.  If your debating opponent demands your acceptance of their predicates, the very predicates that demand debate, then there are no grounds for discussion.

That is the argument Snow reluctantly faced with a bad-faith debater, Leavis.  Leavis was an intellectual who became a crank and eventually only argued based on his beliefs and opinions rather than on logic or evidence.  As always happens, he increasingly ended up defaulting to misdirection, fraud, deliberate misstatements and ad hominem arguments.  

THE CASE OF LEAVIS AND THE SERIOUS CASE 

In his lecture published in the Times Literary Supplement on 23 April 1970 ['Literarism versus Scientism: the Misconception and the Menace'], Leavis refers to 'the debate about [or between] the Two Cultures', and then says — 'There has been no debate.'  The most recent bibliography of this topic that I have seen, compiled in an American university, lists between 1964 and 1968, in the English language alone, eighty-eight separate items.  It would have been more accurate for Leavis to say that there has been no debate between him and me.  There has not: nor will there be.  For one simple and overriding reason.  I can't trust him to keep to the ground-rules of academic or intellectual controversy.  By 'ground-rules' here, I do not mean anything in the least complex or difficult.  If I enter into discussion on any topic, intellectual, moral, practical, or whatever combination you like, it matters very little what I feel for my opponent, or what he feels for me.  But I am entitled to require — or if I am not so entitled then I have to beg to be excused — that he will observe some basic and very simple rules.  If he refers to words that I have said or written, he will quote them accurately.  He will not attribute to me attitudes and opinions which I do not hold, and if he makes any such attributions, he will check them against the documentary evidence.  He will be careful when referring to incidents in my biography, and he will be scrupulous about getting his facts right.  Naturally, I have a duty to obey the same rules in return.  Nothing could be much more prosaic or straightforward; but without these ground-rules any sort of serious human exchange becomes impossible. Leavis has, however, not observed them in his references to me and others.  That is why I will not enter into discussion with him. 

It clearly pains Snow to turn his back on the appearance of a debate but he makes clear the wisdom of doing so when there are no shared bases of trust or rules of debate.

It is marginally reassuring to see such a world-class thinker debating with the same issue we deal with today.

Are there core issues which are valid among at least some BLM, Antifa, Critical Theory, Postmodernism advocates?  Almost certainly.  But we cannot access those issues or the arguments supporting them when the advocates eschew any commitment to evidence, logic, empiricism or good faith argumentation.  As long as their only objective is subjugation and winning at any cost, we are no longer in the realm of a marketplace of ideas and instead are in the blighted heath of blind coercion.

And that is no place for a civilized person to waste their time.