What is wrong with New Left censorship and persecution of their enemies is not that it is an assault on an abstract construct called Free Speech - but that it is the suppression of Good in order that evil may thrive.
The Left, political correctness, the sexual revolution, antiracism, feminism... these are evil ideas; and people who speak in favour of Good are the ones who are being suppressed.
Another linked phenomenon: Hate Speech and Hate Crime laws are obvious nonsense (by obvious I mean that even to try and explain precisely why they are evil nonsense, to argue exactly why they are evil nonsense, is to descend to the level of demonic evil; and if you personally cannot know directly that they are evil, then I'm afraid you are deeply corrupted).
But against the Hate legislation - should we promote Free Speech - should it be defended? Has it, indeed, ever been defended?
No and No. There are many things (perhaps most things) that should not be said, in many contexts - and there should be no onus to prove conclusive harm from them before deterrence or prevention or punishment: once said, it is often too late.
But we are making further assumptions here - false ones. Because another illusion is that it is the specific definable content of 'speech' that needs to be promoted or suppressed: that is not true, that is Pharisee-ism/ legalism/ bureaucracy - which is another evil.
To be clearer - that is what the High Priests did when they took Jesus's saying and actions and chopped them up into decontexualised units, and judged them by abstract generalities from The Law. In fact, Jesus was wholly Good and did nothing but Good - because he was Good everything he said or did was Good, and what these behaviours could be made to seem like when studied in isolation was utterly irrelevant.
So free speech is Not A Good Thing, indeed laws to promote or prevent certain speech content are A Bad Thing - so, if we are not to be guided by laws, rule, content - then what?
I have written about this before. Think again of Jesus - Jesus did (only) Good Things because he was a (wholly) Good Person. And the best-attainable-approximation to that concrete fact is the natural basis of 'law' - or should be.
Good Things are the things done by Good People. Now, nobody is wholly-Good in the way that Jesus was - but some people are much better than others (they have greater Virtue) - some people have or serve evil motivations, are of evil intent (perhaps they seek the suffering or exploitation of others, perhaps they seek the corruption and damnation of others).
The proper guide to regulation of public speech and action is that 'the platform' should be reserved for Good people and Bad people should be excluded. Leave out the specifics, it is the nature, motivation, intention, disposition that matters.
The politically correct/ social justice warriors/ antiracists/ antifa/ feminst/ sexual revolutionaries are quite correct that the proper procedure is to give No Platform - but, as advocates and servants of moral inversion, they use this procedure to promote evil and crush Good.
Those who are Good should Not be promoting Free Speech - they should be censoring, suppressing, deplatforming speech of evil intent - including speech that is intentionally subversive, corrupting - has an agenda of inverting truth, beauty and virtue.
(Would you want an advocate of pederasty to discuss this with your children? If not them, why anybody?)
If you can help it, if you have the power; then Do Not Allow those whom you judge to be the demons or their many/ majority servants and minions to have space or time or resources to address people; to pursue their agenda of evil - whether short-term-tactical evil; or insidious, soft-sell, strategically, deviously evil (which will be done by Bad People deploying - mostly - Good content).
This applies - as a valid and proper goal - as well in small as in great - in blog comments as well as in mass media; among family and friends as in great public halls.