Here’s my melodramatic theory: social media lost Labour the last election and it’s going to lose Labour the next one, too.

It sounds bonkers, doesn’t it? But look at it like this: “political Twitter”, the small subset of the social network that isn’t tweeting about One Direction or surfers being ­attacked by sharks, is undeniably skewed to the left. Twitter probably evolved into lefty heaven as a reaction to the right-wing dominance of the printed press, and because of the many arts and comedy bigwigs who imported their existing followings on to the platform. Most progressive commentators and columnists are on there, tweeting away several times a day, while their right-wing equivalents avoid the service altogether, or venture on very occasionally to share a link to their piece.

Then there’s Facebook, a much bigger fish, which ought to be more reflective of the wider population because it’s made of networks of schoolfriends, former colleagues, and parents and children. But news on Facebook travels through “Likes” and shares, and people won’t Like a crackdown on benefits, even if they secretly support it. A lot of what happens on Facebook, as with Twitter, is “virtue signalling” – showing off to your friends about how right on you are.

It was this “Tyranny of the Like” that had many social media users convinced that Ed Miliband could squeak the election; after all, their friends seemed to be lapping up the mansion tax and the action against non-doms. No one seemed enthused about taking £12bn off the benefit bill, or reducing the help given to disabled people.

Partly this is an advanced version of the “shy Tory” phenomenon that has long led pollsters to underestimate the Conservative vote. The late New Labour guru Philip Gould saw it in focus groups conducted in 1985, where women aged 25 to 44 were asked what issues affected them. They named law and order, health, education and variations on the micro-economy. They didn’t give a stuff about Labour’s preoccupations: nuclear disarmament and the role of minorities in society. Gould concluded: “Self-interest was no longer a dirty word; they admitted openly they looked after themselves first.”

Now imagine those same people tweeting or facebooking their thoughts. Would they be as honest and open about their self-interest? I doubt it. They’d be changing their avatar to a rainbow flag, or ostentatiously sharing the touching story of a girl who needs a new wheelchair but can’t ­afford one. And on 7 May, a large percentage of them would have voted Tory.

This summer, as George Osborne slashes tax credits and makes swaths of southern England off limits to anyone on benefits (thanks to the new £20,000 cap), Labour’s attention should turn to the next election and picking a leader who can beat him.

Instead, a large number of constituency parties are nominating Jeremy Corbyn, even though he doesn’t want to be leader, has never held a leadership position in the party and could never find two dozen fellow-travellers to form a shadow cabinet. Clearly, these CLPs don’t think that Corbyn is their best shot at beating Osborne, overturning his unjust policies and enacting Labour ones instead. They are doing it to signal that they are on the side of right and good.

The American writer Matt Bruenig calls this “purity leftism”. As he wrote in 2012, “When purity leftists do actions and organising, their interest is not in reducing oppression as much as it is in reducing their own participation in it. Above all else, they want to be able to say that they are not oppressing, not that oppression has ended.”

Not all Corbyn supporters are like this. Some are backing him because they think he has the best ideas for the country and want him to challenge the other candidates, or because they admire his many years of ­dedication to his constituents. He is undoubtedly a dogged campaigner, an energetic speaker and a parsimonious public servant.

But I’ve had enough of people describing him as “principled” as if it were a synonym for “holds opinions I agree with”. Liz Kendall, who has been relentlessly called a Tory in disguise – a Facebook Q&A she did was particularly testy on this front – is also principled. If you acknowledge that Corbyn is giving voice to marginalised opinions, you must also acknowledge it takes lady-balls to go to a meeting of Labour activists and say that you support the two-child benefit limit or the 2 per cent defence spending commitment. Kendall is booed at hustings while Corbyn is cheered. Her campaign is faltering precisely because she is saying what she believes.

As it happens, I disagree with her about the two-child limit – in the words of The West Wing’s Josh Lyman, Osborne apparently wants a government just small enough to fit into our bedrooms. But it is undeniably popular with exactly the people Labour was founded to represent.

What Kendall is doing is also more principled – “courageous”, even, in the Yes, Minister sense of foolhardy – than the strategy pursued by Andy Burnham and Yvette Cooper, who will not attack Corbyn head on because they want anyone who votes for him to put them down in second place.

At a recent Gay Pride march, Burnham wore a T-shirt proclaiming that he’d “never kissed a Tory”. Well, if he wants to win the next election he’s going to have to do a bit more than kiss some Tories. He’s going to have to convince them to vote Labour. (That’s third base, at least, in my book.) Will reaching out to those voters be seen as a betrayal, too?

Ultimately, in the secrecy of the ballot, when there’s no more virtue signalling to be done, Corbyn will fade away. But the country will have taken note of a Labour Party that seems to prefer the purity of opposition to the compromises of power.