France does not like the idea of collecting ethnic data because the last time we did it was before we sent the Jews to the concentration camps, going above and beyond the demands of the Nazis. In 1978, the government passed a law prohibiting the collection of ethnic data.
France also does not like the idea of ethnic data because it goes against the myth (because it is a myth) of a unified Republic where all that matters is the national identity. France is not a multicultural country and significant segments of the population (both from the left and right wings of the political spectrum) do not want a multicultural country. They want an assimilationist Republic (that is, one where immigrants make all the efforts to assimilate but nothing is due from the dominant group). The problem is that one of the necessary conditions of assimilation is acceptance of assimilated minorities by the dominant group: that is both cultural and institutional assimilation, which means no discrimination. Many studies have shown this is far from the case and that discrimination, both individual and institutional is widespread.
In this way, France is a very Durkheimian society where the educational system is still very much perceived as the frontline of the Republic (and public school teachers were the main soldiers of the Republicm wrestling young minds from the dreadful clutches of the Church), where children are taught the value of being French and living in a republic and where collective conscience is clearly internalized. Not a big surprise here: Durkheim was very instrumental in the development of the French public system of education.
As a result, France is notoriously hostile to policies such as affirmative action which are perceived as promoting communautarianism and separatism, that is, the slicing and dicing and allocation of rights and benefits along ethnic lines (France already allocates many benefits either universally, such as the health care and educational systems as well as family benefits, or on the basis of income). This deeply-held attitude is the basis for the controversy over the veil in schools and demands for special privileges by some Muslim groups.
There is no doubt that the current economic situation will not provide a calm context for rational discussions of immigration policies and persistent discrimination.
Such nationalist fears of national undermining from within are also accompanied by fears of undermining from above, notably through assimilation into the European Union. As much as mainstream political parties have made France a main engine of the European Union (along with Germany), there has always a clear and vocal anti-EU current in French politics, both on the left and the right reflecting fears of imposition of neo-liberal policies along with fears of the loss of cultural specificity (don’t touch my camembert!).