At the start of this year, the school in the little French town of Sargé-lès-le-Mans instituted a “pork or nothing” policy. Muslim and Jewish kids have either to eat pork or go hungry. Apparently this move is necessary to “save secularism”, according to National Front leader Marine le Pen. “We will accept no religious requirements in the school lunch menus,” she said. “There is no reason for religion to enter the public sphere.”

The glorious triumph of atheistic rationality over the dangerous totalitarian obscurantism of the Catholic church is one of the great foundation myths of republican France. And coded within this mythology is the message that liberty, equality, fraternity can flourish only when religion is suppressed from the public sphere. It is worth remembering what this ideological space-clearing involved.

At the end of the 18th century, France’s war against the Catholic church reached its bloody conclusion. By Easter 1794, the same revolution that once proclaimed freedom of conscience had forcedly closed down the vast majority of France’s 40,000 churches. What began with the confiscation of church property and the smashing of crosses and chalices, ended with forced conversions and the slaughter of priests and nuns at the guillotine.

It is in this period, the so-called Reign of Terror, that the modern English word terrorism – deriving from the French terrorisme – has its origins. “Terror is nothing but prompt, severe, inflexible justice; it is therefore an emanation of virtue,” argued Robespierre, in what now sounds like a sick press release from Islamic State. Over in the Vendée, those who remained loyal to their centuries-old faith were massacred in what historian Mark Levene has called “an archetype of modern genocide”. The systematic de-Christianisation of France was not the natural and inevitable collapse of sclerotic religion and the natural and inevitable rise of Enlightenment rationality. It was murderous, state-sponsored suppression.

Of course, there are those who think the Catholic church had it coming. Yes, it had cornered a huge proportion of France’s wealth. Yes, it had a dangerously symbiotic relationship with the monarchy and reactionary aristocrats in powdered wigs. But these days, the Catholic church is no longer any political challenge to the French state. And the reason publications such as Charlie Hebdo persist with their crass anti-clerical cliches (where the joke is usually a variation on bishops buggering each other) is that a powerful strain of French self-understanding actually requires a sense of external religious threat against which to frame itself. But as the Catholic church is no longer planning to sponsor a coup against the state, Republican identity requires something new to define itself against – something just like radical Islam. As Voltaire put it: “If God did not exist it would be necessary to invent him.” Thus France picked a fight with Islam by banning the headscarf from schools in 2004 and the niqab from all public life back in 2010 – bans which closely echo the hostility of earlier generations to the veiling of nuns.

But there is a huge difference between targeting grand bishops in Rome and a beleaguered, economically fragile Muslim community that has received a great many knocks at the hands of the French state and its colonial past. Rabelaisian derision aimed at the House of Saud or Abu Bakr al-Baghdadi is one thing. But aimed at the disaffected banlieues it is bullying and goading. You have to be suspicious that French secularism is not the neutral thing it purports to be when racists such as Le Pen start defending it so enthusiastically. And yet there is nothing the leaders of al-Qaida want more than the French state to be seen to declare war on its religious citizens once again. They know that many young, disaffected Arab immigrants on the sink estates outside Paris are itching for a fight. The French government must not give it to them. And that means re-thinking their precious laïcité.

@giles_fraser