In 2008 there were some 4 million Muslims in France, representing 6.4% of the population (based on the Trajectories and Origins study published by Ined and the Institute of Statistics and Economic Studies [Insee] in 2008). Common sense suggests that 4 million people are not going to upset our way of life, our relationship with religion and our social advances, some still very recent.

Among young adults, just over one in 10 of the population is a Muslim. In the 18-50 age group in France there is one Muslim for every four Roman Catholics. Focusing attention on the most fervent believers in this age group, those who attach great importance to their faith, Muslims outnumber Catholics by about 150,000. Among those born in France in the 1980s, the ratio is three to one. Islam is gaining ground in France where Christianity has already substantially declined. Succeeding generations of French origin are getting more secular in their outlook. In 2008 about 60% of youths said they had no religious belief.

The pattern among the children of immigrants from north Africa, Sahel and Turkey is the opposite, with religion gaining in importance, particularly among the young: in 2008 only 13% acknowledged that they had no religious belief. In 1992, a third of people aged between 20 and 29 and born of two Algerian-immigrant parents admitted having no faith. In 2008, in the same age group, only 14% of those surveyed had no faith.

Islam is riding on a more favourable population dynamic than Catholicism: a large proportion of young people adopt their parents' religion, few marry outside their religious community; the birthrate is high and immigration will certainly continue. Furthermore, Muslims are highly concentrated in large cities, increasing their visibility and their ability to mobilise: in 2008 more than two-thirds of France's Muslims were living in urban areas with 200,000 residents or more, compared with 40% of members of other religious groups or non-believers. In the Seine-Saint-Denis département, north-east of Paris, Muslims now constitute the largest religious community.

Although there is little chance the French will all convert to Islam, its influence is already visible in religious affairs and in certain districts. France thought it had done with religious matters; Islam has put them back on the agenda. We tend to think that secularism is spreading, like some irresistible historical trend, so we see any contrary movement as an aberration that can only be explained by alienation and despair. We consider the growing influence of Islam as a sickness: to cure it we must treat not its symptoms but the social misery at its root.

This attitude offers three advantages: it sustains an illusion about the nature of the problem, it offers a familiar solution, and it leaves intact our belief in the inexorable progress of secularisation. Strong in this conviction, it seems inconceivable that Islam might change our way of life. The perception of Islam as a victim is narcissistic – we are the cause of the Other's misfortune – and condescending, the Other being deprived of the willpower and capacity to choose. Such an attitude is part of a relativistic era that prevents us from passing judgment on practices we might once have condemned, and that encourages us to open up to outside influences. The same process leads us to disregard moderate Muslims, who are rather too much like ourselves, and prefer those whose only form of moderation is to reject the use of violence in defence of their cause.

Islam is still a minority religion, but it has already changed our freedom of expression, an essential part of democracy. The fear of being catalogued as xenophobic or Islamophobic – despite being one of the favourite weapons of radicals in their fight against freedom of expression, this concept has enjoyed considerable success in the west – has been reinforced by intimidation, especially over school syllabuses. Since the Salman Rushdie affair, the idea of stirring up racial hatred has been turned upside down, and our key concern now seems to be to avoid provoking a violent outburst by the advocates of Islamic norms each time they take offence, as happened over the Danish cartoons.

• Michèle Tribalat is a French demographics expert who specialises on
immigration issues

Gérard Mauger

A spectre haunts policymakers, journalists, sociologists, and experts in thinktanks: "the social question", in its contemporary form of mass vulnerability and increasingly widespread zones of disaffiliation. For the past 30 years France's banlieues – underprivileged housing estates plagued by poverty, and emblematic of the crisis in the working classes – have been in the headlines, high on the political agenda and in invitations to tender addressed to social scientists.

Relocation of whole branches of industry and the transformation of working practices have ruined traditional working trades and brought unemployment, poverty and casual labour to the margins of the working classes, depriving the workforce of its economic value and devaluing more symbolic concepts such as virility, which played a central role in defining traditional working-class male identity. But the lower classes have not disappeared, as some would have us believe: the decline in the number of workers – almost a quarter of the active population – is partly compensated by the spread of manufacturing jobs now classified as services.

The ever more precarious predicament, the determination to guard against unemployment and loss of social status, and the aspiration towards better conditions, all explain the quest for social improvement through higher education, at the same time as the declining appeal of vocational training in favour of more academic studies. Failure at school condemns people to stay working class. Carrying on with education maintains the illusion of possible advancement. But despite their efforts, most students at vocational secondary schools achieve little long-term job security.

How are we to understand the transformation of former red suburbs into sink estates? The massive rehousing programmes of the 1960 and 1970s hardened the divide between semi-skilled workers and immigrant labourers, and their highly skilled counterparts, for whom getting a new home symbolised collective advancement. During the late 1970s, housing policies made it easier for working-class families to buy their own homes, leading to a mass exodus from social housing by better-off households. No longer synonymous with success, the large housing estates lost their appeal.

The place of those who left was soon taken by immigrant families, further accentuating the division between home-owning and housing-estate workers. Towards the end of the 1970s, the downturn in the economy affected the least well qualified workers and the most recent immigrants. For working-class households, staying in low-income housing reflected the precarious nature of their employment. It was also the physical manifestation of their equality with the newcomers.

With no way out of their estates, these workers often became the advocates of stricter law and order, particularly for local youths. When immigrant families first arrived on the estates, it seemed an improvement on their previous temporary housing, but later they came to fear that their sons might stray outside the law.

Public perception of these problem estates is coloured by recurrent social ills: breakdown of law and order, and difficulties with integration. In both cases the problems are explicitly connected to immigration.

In this way the social question, which caused such estates in the first place, has turned into an immigration problem. The efforts of France's far-right National Front (FN) party and the right wing of the governing centre-right UMP party have ensured that the "immigration question" stays near the top of the political agenda. The transformation is all the more successful because there is a real basis for these problems: in the estates there is plenty of scope for delinquency to flourish.

As for the problem of integration and the ongoing controversy about the (republican) French model and its (multicultural) Anglo-Saxon counterpart, it finds much of its justification in the Islamic revival in underprivileged neighbourhoods.

Traditional forms of working-class organisation in the red suburbs east of Paris have been replaced by new forms of collective or religious action, ranging from big brothers to imams. Imported from the black ghettos of the US, hip-hop is now the dominant culture among young people on the estates for at least three reasons: it brings into play forms of language and gesture that are purportedly theirs to own; the rappers have, to varying degrees, succeeded in voicing the woes of underprivileged youth; last, and perhaps most important, having been taken on board by the dominant culture, hip-hop seems to offer the means of achieving symbolic rehabilitation, and maybe even the promise of riches.

Confronted with the discrepancy between the social status to which they aspire and the empty promise of their degrees, with discrimination in the market for jobs and housing, and with everyday xenophobia, a few young Muslim graduates have decided to act.

They reject the image of poor wretches, constantly in trouble with the police, who know neither how to behave properly nor how to control their children. They also reject the idea of "secondhand Arabs" who hold down executive jobs, no longer speak Arabic and have native-French partners. Instead they are reconstructing their identity, a process that gives additional importance to the community, to campaigns to restore the use of Arabic, and of course to religion.

Islam's message may strike a chord with some youths living on underprivileged estates, but the reasons for this are to be found in its symbolic value, its power to transform the stigma associated with being an Arab into a value of choice, synonymous with the pride of being a Muslim.

Importing the multicultural model has transformed a social question into a racial issue, substituting a perception of society with class divisions with a mosaic of ethnically differentiated communities, and in so doing strengthening divisions among the working classes.

• Gérard Mauger is a French sociologist and director of research at the CNRS

These articles originally appeared in Le Monde