Regardless of how many MPs reject the idea of a no-deal Brexit, or how often, the legal fact remains that Britain’s EU membership expires on 29 March. Parliament cannot unilaterally change the date, so the British government is as dependent on a functional dialogue with the EU in the aftermath of Theresa May’s deal having been rejected as it was when the deal was being negotiated.

That should be obvious, but a remarkable number of MPs still appear not to understand basic facts about Brexit. Conservatives in particular struggle to process the point that a Brexit plan cooked up in a Westminster corridor is worthless if there is no prospect of it being viable in Brussels.

A case in point is the “Malthouse compromise”, named after its architect, the housing minister, Kit Malthouse. Britain would leave the EU without a deal but write a cheque for outstanding budget obligations in exchange for a transition like the one in Mrs May’s deal. The UK would ask Brussels to simulate the operation of laws and treaties that would not in reality apply, pretending there was a deal in the absence of one. It embarrasses Britain that senior politicians imagine the EU indulging such a notion. It has already been rejected.

Yet this infantile delusion commands sufficient admiration among Tories that the prime minister felt obliged to offer her MPs a free vote on it.

164 supported the fantasy proposition. Astonishingly, cabinet ministers were among them.

It is harder to judge exactly how many Tory MPs are itching to quit the EU with no deal promptly on 29 March. A government motion that would have exposed that number was successfully amended, simplifying the question and rejecting no deal under all circumstances. That amended version passed by 43 votes.

Not all of those who wanted to keep a no-deal outcome in play think it would be a good thing. Many know it would wreak havoc with the economy, ripping up supply chains, spreading epidemic uncertainty and shredding the UK’s international credibility. It is a stupid idea and not everyone who voted in favour of it is stupid. Some are just cynical. They want to be seen as the sort of devoted Eurosceptic who pursues Brexit at any price. There are career advantages in a party where that kind of zeal is admired. There are fewer rewards for moderation.

Mrs May has not been wholly captured by the cult of no-deal, but she was unwilling in Wednesday’s votes to exclude it from the picture entirely. She has indulged colleagues who advertise “WTO rules” as an alternative framework allowing Britain not to bother negotiating trade with continental neighbours. No developed country uses that model.

The government also published details of the provisional tariff regime that would apply in the event of no-deal. The schedule would have all manner of price implications, with some markets flooded with cheap imports and others protected, yet it was concocted without consultation or transparency. The question of Northern Ireland is addressed with a special tariff-free zone that would invite smugglers to game price differences across the Irish Sea. The plan gives no confidence that Britain’s economy and its institutions would be resilient when faced with the multiple crises that a no-deal scenario would provoke. It is welcome that parliament has, once again, recognised that fact and voted against the idea. But that decision changes very little about the underlying political dynamics of Brexit.

The more revealing aspect of Wednesday’s debates is to confirm that scores of Conservative MPs, including ministers, will eagerly endorse ridiculous, dangerous ideas. They expose themselves and their party to international contempt. They disqualify themselves from being taken seriously in the discussion of how to navigate the country out of its present crisis. The prime minister should exclude them on that basis. To be an enthusiast for no deal or the cockamamie “Malthouse” plan are litmus tests of the judgment and responsibility necessary to hold public office. An alarming proportion of the Conservative party failed.