For some Labour people, there is one consolation to be found amidst the smoking ruin of the party’s devastating election defeat. Such a cataclysm surely has to mean the termination of the party’s fatal experiment with Corbynism.

Or does it? The Corbynites don’t think so. They show scant contrition for what they have inflicted on Labour and the many millions of people who depend on the party to protect and champion them. Nor are they displaying any willingness to relinquish their control. Quite the reverse. Jeremy Corbyn is squatting on as leader while John McDonnell tries to fix the succession for his protege, Rebecca Long Bailey. The senior apparatchiks of the Corbynite court continue to draw their salaries even as the party plans to sack blameless junior Labour staffers and its defeated MPs roar with rage. If Labour is to have any possibility of becoming a competitor for power at some point in the future, the party will first have to be prised from the cold grip of the hard leftists who have controlled its commanding heights for nearly five years.

Another sign that they will not let go without a fight is their extreme reluctance to take any responsibility for the electoral apocalypse that they engineered. Mr Corbyn displays a typically attractive combination of preening self-righteousness and self-exculpation when he insists that he “won the argument” even after smashing the party down to its lowest level of parliamentary representation since 1935. This is worse than risible. It is also characteristically irresponsible and wilfully destructive. He will have done his final disservice to the party if he succeeds in deceiving Labour members into believing that this defeat wasn’t so bad after all.

Let there be no doubt. Labour has suffered one of the most crushing routs in its history. This fourth consecutive election defeat came at the end of an austerity decade presided over by the Conservatives and one in which the Lib Dems were heavily implicated. The Tories also spent much of that time waging an uncivil war with themselves. This election should have been there for the taking and yet Boris Johnson is smugly enthroned back in power with a majority of 80 while Labour contemplates at least another half-decade in opposition.

‘Jeremy Corbyn is squatting on as leader while John McDonnell tries to fix the succession for his protege, Rebecca Long-Bailey.’ Photograph: Phil Noble/Reuters

Much effort is being spent picking through the rubble of the “red wall” seats in the Midlands, the north of England and Wales where Labour’s vote collapsed. This is understandable because it is sensational that Tory MPs now sit for constituencies that had been Labour since the 1930s in many cases and, in some, Labour for ever before the cataclysm of 12 December. The focus on these seats has distracted from just how terrible this election was for Labour elsewhere. In Scotland, the party is back down to just one lonesome MP. So much for the original Corbynite promise that Labour only had to offer a radical left programme and Scots would swoon into the party’s arms. Because there has been so much other wreckage to goggle at, only a few sharp-eyed commentators have noted how atrociously the party performed in election-swinging seats in middle and southern England, seats that have to be won if the party is ever to see the inside of government again. In Northampton, Nuneaton, Swindon, Watford and too many other places to mention, slim Tory majorities have waxed into much fatter and safer ones.

The Corbynite excuses for their colossal failure have come in thin and fast. Blame the media is the laziest. Yes, a lot of the media were hostile to Labour, but since this has always been the case and always will be, any half-competent leader has to have a plan to deal with it. The worst trashing of the brand was not perpetrated by the Tory press, but by the Corbynites themselves. Carrying on what Ed Miliband stupidly started, they relentlessly vilified the Labour government of 1997 to 2010. It was harder to ask for a vote for Labour when it had nothing good to say about the last time it commanded power.

Another favoured Corbynite alibi is Brexit. It is true that Brexit placed great stress on Labour’s electoral coalition. The test of leadership was to manage those strains successfully. The fractures were instead made more acute because the leader was a furtive Brexiter whose unwillingness to pick a side reinforced the other doubts about his fitness to be prime minister. Labour’s vote fell in Leave seats. It also went down in Remain seats. We should not forget that the Conservatives’ electoral coalition was also stressed by Brexit. Recall that 21 Remainer Tory MPs were purged for rebelling before the election. The Conservatives won because they kept most of their vote together while also taking support off Labour. Millions of Tory Remainers backed Boris Johnson when they might have done something different had Labour been under more appealing and less scary leadership. As much as many of them found Brexit appalling, these critical voters found the idea of a Corbynite government even more repulsive.

‘Tony Blair achieved a majority of more than 18,000 in Sedgefield when he won his third election as prime minister in 2005.’ Photograph: Stefan Rousseau/PA Archive/Press Association Ima

The more sophisticated Corbynites argue that the crisis in the party’s heartlands has been gestating for years. There’s something in this, although it doesn’t explain the big anti-Labour swing in many other areas of the country or account for why alienation in the heartlands became so much more severe under Labour’s current management. Tony Blair, the last Labour leader to assemble a winning alliance of working- and middle-class voters, achieved a majority of more than 18,000 in Sedgefield when he won his third election as prime minister in 2005. Corbyn’s Labour has turned Sedgefield blue and installed a Tory MP with a majority of more than 4,000. Nor is there any Corbynite explanation for why Labour’s former voters in the working-class heartlands decided that the answer to their problems was to vote for a Latin-quoting, London-based old Etonian. Both the polling evidence and the reports from Labour candidates tell us that Mr Corbyn was a massive liability. Voters did not trust him with either the economy or security and were baffled and appalled by his associations with extremists and his preference for any repressive dictatorship that called itself leftwing or anti-western. His Kremlin-sympathetic response to the Salisbury poisonings was one of the events that crystallised that distrust, as even some of his disciples now finally acknowledge, a little late in the day.

It is a mistake and a trap to land all the blame on him alone. That is too convenient for the many others who enabled this catastrophe by cheering him on as he led Labour towards the abyss, or were complicit by staying silent when they should have spoken up. Heaping all the culpability on one man will ultimately suit the continuity Corbynites seeking to install one of their own as the next leader. They will say there was nothing wrong with Corbynism except Corbyn. Brilliant experiment – shame about JC. We only have to get ourselves a Corbynite leader “without Jeremy’s unfortunate baggage” and we are all set to win in 2024. This will be their version of the Marxist’s favourite excuse for communism’s multiple failures. There’s nothing wrong with Corbynism; it just hasn’t been tried properly.

So others contesting for the leadership need to be very clear with the party’s members that there was a lot more wrong with Corbynism than its frontman. It was not solely his fault that Labour became so noxious to so many that it simultaneously repelled traditional supporters and swing voters. It was not just the man, it was the far-leftist ideology and the sectarian culture around that man that did it. Corbynism promised a “kinder, gentler” politics, only to make the party hideously nasty in the eyes of anyone who had not imbibed the cult’s flavour of Kool-Aid. Corbynism promised a party answerable to the members only to concentrate all the power in the hands of a tiny cabal of pseudo-revolutionary socialists and fellow travellers. Corbynism fomented a sickness that facilitated the poisonous spread of antisemitism. Corbynism unleashed a factional zealotry that preferred to hunt down internal heretics who deviated from the true faith and brand them as “Tories” rather than try to win converts amongst the electorate. Corbynism preferred to be a glorified protest movement complacently luxuriating in a narcissistic conceit of its own moral superiority rather than do the hard and honest thinking required to secure office. Corbynism produced a fantasy programme that voters found literally incredible.

The election result was a comprehensive rejection not just of Jeremy Corbyn, but the ideology and culture to which he gave his name. Only if Labour confronts and grasps this truth will it have any hope of rebuilding itself as a serious contender for power.

• Andrew Rawnsley is Chief Political Commentator of the Observer