Alain Finkielkraut:
Laicity is the solution that modern Europe found in order to escape its religious civil wars. But contemporary Europe doesn’t take religion seriously enough to know how to stick to this solution. She has exiled faith to the fantastic world of human irreality that the Marxists called “superstructure”. . . thus, precisely through their failure to believe in religion, the representatives of secularism empty laicity of its substance, and swallow, for humanitarian reasons, the demands of its enemies.
I haven't read anything by Finkielkraut except the above and a few other excerpts translated and edited by Ann Sterzinger. But that won't stop me from explaining what I take to be the brilliant insight embedded in the above quotation.
Laicity is French secularity, the absence of religious influence and involvement in government affairs. This absence has had the salutary effect of preventing civil strife over religion. But to appreciate why laicity is important and salutary one must understand that the roots of religion lie deep in human nature. Religion is even less likely to "wither away" (V. I. Lenin) than the State. Leftists, however, are constitutionally incapable of understanding that man by nature is homo religiosus and that the roots of religion in human nature are ineradicable.
The Radicals don't understand the radicality (deep-going rootedness) of religion. (Radix is Latin for 'root.') In their superficial way, leftists think that religion is merely "the sigh of the oppressed creature" (Marx) and will vanish when the oppression of man by man is eliminated, which of course will never happen by human effort alone, though Marxists fancy that they can bring it about if only they throw enough people into enough gulags. Leftists cannot take religion seriously and they don't think anyone else really takes it seriously either, not even Muslims. They don't believe that most Muslims really do believe in Allah and the divine origin of the Koran and the 72 black-eyed virgins and the obligation to make jihad. They project their failure to understand religion and its grip into others. See my Does Anyone Really Believe in the Muslim Paradise in which I report on the Sam Harris vs. Scott Atran debate.
The issue at present is not whether religion is true but whether it answers to deep human needs that cannot be met in any other way. My point is not that leftists think that religion is false or delusional, although they do think it to be such; my point is that they don't appreciate the depth of the religious need even if it is a need that, in the nature of things, cannot be met. Again, man by nature is homo religiosus just as he is, by nature, animal rationale, zoon logikon (ζῷον λογικόν, Aristotle).
Not understanding religion, leftists, not to mention some conservatives, fail to understand how important laicity or secularity is to prevent civil strife over religion. And so they don't properly uphold it. They cave in to the Muslims who reject it. Why don't they understand the dire existential threat that radical Islam poses to European culture? I suspect that it is because they think that Muslims don't really believe in all their official claptrap and that what Muslims really want are mundane things such as jobs and material security and panem et circenses. They cherish the foolish leftist belief that 'deep down' we are all the same and that Muslims want the same things that decadent Europeans want. They make the common but very foolish mistake of projecting their values, attitudes, and presuppositions into others.
In nuce: leftists, who are resolutely secular, fail to uphold the secularity that they must uphold if they are to preserve their loose and libertine way of life, and they fail to uphold it by failing to understand the dangers of religion, dangers they do not understand because they fail to take religion seriously and to appreciate the deep roots it has in human nature. Here is an even pithier formulation:
Leftists, whose shallow heads cannot grasp religion, are in danger of losing their heads to radical jihadi. This is cause and effect of the lapse of laicity.
Two quibbles with Finkielkraut.
First, it is not that leftists "do not believe in religion," but that they do not believe that religion is a powerful and ineradicable force in human affairs. You don't have to believe in religion to believe facts about it.
Second, for Karl Marx, the superstructure (Ueberbau), though a repository of fantastic ideas devoid of truth such as religious ideas and the ideas of bourgeois law and morality, also contains all ideology and therefore the 'liberating' Marxist ideology as well. It too is a reflection of the Unterbau, the social base and the means of production. So not everything in the superstructure is "fantastic," as Finkelkraut implies above. This Marxian notion that all is ideology including their dialectical ‘science,’ leads to relativism, but that's not my problem.