For most people France embodies an exception among the other European countries and that exception is linked to the supposedly antireligious character of the French state since the French Revolution of 1789.
Historically, in fact the relation between the French Church and the French state started to change four centuries before 1789, with Philippe Le Bel in the 14th century. The French monarchy struggled to become independent form the Roman Catholic Church. Not because the King of France was antireligious but because he wanted to control the Church from above. In exchange the French Catholic Church got very important privileges in terms of taxes, primary role in education, etc., a situation which lasted until 1789.
Many people think that the Enlightenment (philosophers like Rousseau, Diderot and Voltaire) were atheists. They were not : they were against the power of the Catholic Church, which is very different. Was the French Revolution against religion ? No. Robespierre even created the « Cult of the Supreme Being ». French revolutionaries (with the exception of Jacques Roux and his Enragés) wanted only the Church to recognize the new political authorities and the new laws. They prosecuted only the priests (the majority of them, to be honest) who rebelled against the political and social changes of that period.
And the reason why an important part of the workers movement became not only anticlerical but antireligious is linked to the political attitude of the French Catholic Church in 1789, 1830, 1848 and 1871 (the Paris Commune).
During all these revolutions, the Catholic Church took the most reactionary positions, favoring the royalty, the most conservative aristocrats, etc. The Catholic Church refused to recognize freethinking ; the « Declaration of the Rights of Man » was considered « impious ». For the most traditional catholics freethinking was an « insurrection against God ». The Catholic Church refused to understand the social dimension of the revolutionary events : for the Church they were the expression of « wild and evil passions ». And this sectarian attitude contributed to nourrish strong anticlerical feelings. Before the Dreyfus Affair (1894-1899), anticlericalism was one of the most important element structuring the French Left. This peculiar situation explains why there was a political alliance between the working class movement (i.e. the anarchists, the Socialist Party, the revolutionary syndicalists leading the main trade unions) and a part of the bourgeoisie and petty-bourgeoisie organized into the Parti Radical. This Party was violently anticlerical but not antireligious ; it had strong ties with the Free Masons and designed the law adopted in 1905 about the separation between the different churches and the state, law which is portrayed, one century later, as an antireligious law.
Since 1905 a whole mythology is born in France affecting both the workers movement and all the main bourgeois parties : the myth of the superiority of French secularism. And this myth has often united the left and right wing parties, in their praise of socalled Republican virtues.
The cult of the secular Republic is the basis of left and right wing nationalism ; it’s the cement of national unity ; it is the foundation of the joint myths of Gaullist and Stalinist Resistance movements ; so this is why, in their speaches, the Right and the Left wing parties still maintain an anti-multiculturalist posture, even if in practice they defend quite different politics.