Three types dominate extremist movements: crazies, cynics and creeps. The true crazies are always at the bottom of the heap. Cynical propagandists stoke their righteous fury, without which the extremist movement would collapse. Creeps rise to the top, in extremist movements as elsewhere. They are cynical, too, of course. They know how to manipulate their base. But they must show signs of authentic craziness as well or their grip on leadership would weaken and others would take their place.

Crazies, cynics and creeps. Of the three, the cynics are the easiest to understand. They live in the conspiratorial world of clickbait journalism where charlatans churn out fantasies for sites as various as the Telegraph and the Canary. Asking if they believe their propaganda is like asking a lawyer if she believes her client is innocent. It helps, but it is beside the point. What matters is not whether they are sincere, but whether they can fake sincerity like any other salesman or woman with a product to market.

Cynics now manipulate the fate of nations. But once they were dismissed. From the fall of the Berlin Wall until 2016, polite society believed it could safely allow the extremes to fester. The far left would never take over the Labour party. The nationalist right would never take over the US Republicans or British Conservatives. If they did, sensible voters would reject them. Hillary Clinton would always beat Donald Trump. The British would always prefer the European devil they knew to a dangerous, uncertain future.

In this complacent environment, mainstream politicians and commentators assumed that every variety of cynic – and crazy and creep – could be bought off. David Cameron assumed he could appease the right by giving them a referendum “everybody” knew he would win. The centre left never bothered to fight the far left because “everybody” was equally certain that it was an irrelevance.

Allow me to let one shabby figure stand for a neglected underworld. For years, Christopher Booker of the Sunday Telegraph fanned every ignorant prejudice on the right. He denied manmade global warming. “Arctic ice isn’t vanishing after all,” he declared in 2007. (It is now vanishing so fast its absence is destabilising the entire global weather system.) He maintained Darwin’s theory of evolution was no better than creationism. Inevitably, he treated the EU as if it were a dictatorship. It seemed that no falsehood was too gross for him to circulate. At one point, he told his appreciative readers that the EU would not allow us to bury our pets until we had put them in a pressure cooker and boiled them “at 130 degrees centigrade for half an hour”.

Yet when Telegraph readers took him at his word and voted to leave behind the EU’s bunny boilers, Booker was consumed with fear. Quitting the EU-dominated European Economic Area, with the freedom of movement and compliance with EU laws Brexiters say they abhor, could lead Britain to the “ultimate disaster” of being alone in the world without agreements to trade with the EU or anyone else.

“No, no, no,” he seemed to be crying. “Surely you didn’t believe me when I said the EU would make you cook your pets. How crazy are you crazies?”

You might think that Booker is a ridiculous man not worth wasting time with. Once, you would have been right. Now he is no different from our rulers. A majority of MPs also believe it would be a disaster for Britain to leave the EU without securing membership of the single market or the customs union. Last week, they nevertheless gave Theresa May the power to negotiate just that. Hack journalists say they are just giving the readers what they want. Our politicians say they are just giving the 52% who voted to leave – now redefined as “the people” – what they want.

Respectable opinion cheers them on and holds that bowing to “the people” is the only available option. Perhaps they are right.

Perhaps, in 18 months’ time, MPs who suppressed their consciences and silenced their doubts will be able to say: “How crazy are you crazies? You didn’t actually believe we were sincere when we voted for Brexit in the Commons. No, no, no, we thought it would be a disaster all along. But we had to give ‘the people’ what they wanted.”

Perhaps “the people” will accept their excuse and blame themselves for Britain’s plight. Political “leaders”, who can only follow, must hope that they do, even though it is an iron law of democracy that “the people” never blame themselves.

Do not forget that Brexit has made cynics not just of the majority of the parliamentary Labour party and supposedly moderate Tory MPs, but of Theresa May. She is taking Britain out of the European Union when she voted in favour of Britain staying in the European Union.

I cannot think of any prime minister in British history who has behaved more cynically on a great issue of state. But her example shows that leaders cannot just be cynics. They have to do more than merely manipulate their crazies. They must creep to them and become like them. So we have the spectacle of Donald Trump’s furious tweets against the judges who have struck down his immigration bans. On the one hand, it is a cynically calculated strategy. Trump will be able to blame any terrorist attacks on the US judiciary, although no one who understands terrorism believes his edicts would save a single life. But at the same time his accusations of treason, his anti-Muslim bigotry and his contempt for the rule of law match the craziness of his supporters. He both manipulates them and is one of them.

Equally, Theresa May has to feel the zeal of the convert. To make up for her cynical espousal of a cause she once rejected, she must not only manipulate Ukip and the Tory right but become Ukip and the Tory right and enthusiastically endorse the most uncompromising Brexit on offer.

Those who look with horror at the disastrous movements tearing through western societies should relearn a lesson that should never have been forgotten: you have to fight the cynics and the crazies and the creeps from the moment they appear. Do not think that you can ignore the extremes, as the centre left did, or buy them off, as Cameron thought he could.

If you do, they will come for you and you won’t know how to fight. You won’t even know why you must fight, until it is too late.