A former leader of the Conservative party, Iain Duncan Smith, posts pictures of his vandalised constituency office online. This provokes an avalanche of vicious abuse and threats of violence against him and his family.

The tidal wave of messages, arriving so fast that they seem suspiciously mechanised, ranges from the malicious to the bizarrely unhinged. It features the death threats that have become part of the standard currency of social media and which necessitate police intervention. This is now so commonplace that it has become a boring story.

These attacks are specific in their political targeting even when they are hysterically incoherent: Tories are mass murderers. They deserve to be persecuted and tortured, and so on and on. Given the almost instantaneous coordination of such campaigns, they are clearly being orchestrated if not by bona fide Labour activists then certainly by their camp followers.

I can remember a time when the socialists were supposed to be the nice people and the Conservatives even cast themselves as the “nasty party”. Whatever happened to that?

Of course some of this is simply the eternal crank mob finding a home. The guys in their underpants sitting in bedrooms surrounded by empty pizza boxes have suddenly discovered that they are not alone.

But most of it has a more interesting explanation. The hard Left is actually, genuinely losing its mind. The full reality of the collapse of communism has finally led to the nervous breakdown that it was bound to produce in its dedicated following in the West.

This wild convulsive flailing of the beast as it sinks into irrelevance (what Trotsky might have called the “dustbin of history”) has taken nearly a generation to materialise but here it is at last. What we are living through is the last desperate twenty seconds of the Marxist dream.

You may think: so what? The hard core totalitarian Left was always a small minority in this country. Most people who voted Labour regarded it as a sideshow. Don’t worry – we will survive this momentary spasm of Orwellian organised hate and get back to the realm of rational discourse and decency that has traditionally characterised the disagreements between Left and Right in Britain.

There are two problems with this. One is ideologically less important but socially more destructive. That is that the hate-mongering of the Left could license the lunatic far Right which, of course, is still a real presence too. Before it finally dies out, this pathological demonising of the political adversary may provoke an equal and opposite reaction and we will end up with the sort of mayhem on the streets that is so alien to the national character.

At a time of terror threats and random attacks like the London Bridge incident on Friday, this could only add to a pervasive sense of vitriolic anarchy.

I don’t believe such a meltdown to be an imminent danger, revering as I do the British capacity for maintaining sanity under pressure, but the provocation is becoming so incendiary and the public dialogue so degraded, that it cannot be ruled out. The more lasting worry is for the condition of the Left as a plausible democratic alternative. However unsympathetic you may be to Labour, its disintegration as a viable opposition leaves a critical vacancy in our political life.

I can hear you objecting that this dilemma is just a temporary aberration: when Labour loses this election (or even if it doesn’t) Jeremy Corbyn will be replaced as leader and the party will go back to being the consensual moderate semi-socialist force that used to be a fixture on the British scene.

There is, however, an immediate difficulty with this comforting scenario: the hard Left machine now has a firm grip on the levers of the party at every level. It can choose new parliamentary candidates and effectively deselect sitting ones. With the support of its trade union sponsors, it can determine party policy and control appointments to its executive bodies.

Certainly it is not theoretically impossible to remove this junta but it is going to take years of dedicated effort – and matching the disciplined concentration of that entrenched hard core Left will be quite a project. These are people who devote their every waking moment (quite literally) to activism of both the overt and covert kind.

That is why they run circles around traditional party operations and conventional news outlets. (The BBC is particularly clueless about their ability to infiltrate supposedly “balanced” public audiences and panels.) This task will be made even harder by precisely the desperation I have described.

It is widely understood on the hard Left that this communist take over of the shell outfit previously known as Labour is its last chance. Once its fingers have been prised off this vehicle, it will be finished. Make no mistake, this is going to be a fight to the death.

But more broadly, what is the future of the soft Left idea?

Through the Cold War years in the West, East European totalitarianism was an acknowledged threat, but there were perfectly acceptable democratic socialist possibilities. Now that the Eastern version has come to an ignominious end, what exactly remains of the economic theory on which the soft versions were parasitical?

The Eastern command economies kept their populations in poverty while Western free markets produced mass prosperity. The redistribution of wealth was a fiction because, once seized by the state, the production of wealth collapsed.

Enforced equality meant the destruction of individual freedom. What is left of democratic socialism if the most basic Marxist concepts are discredited? Gordon Brown, the last man in Britain to try and make this work, was reduced to talking in paradoxical riddles: using the “proceeds of (free market) growth” to produce “social fairness”.

And that ended up satisfying nobody – or, as the Marxists used to say, it collapsed under the weight of its own contradictions.