Good policy. France is ethnically divided. A civil war in the next 50 years is more likely than not. This is a last ditch attempt to create a sense of national unity by subjecting everyone to mass indoctrination by the last vestige of conservative authority in the country (the military). I hope it works. If it fails, at least the indigenous population of France will have gained some needed military skills, otherwise they would be hopeless against France's non-indigenous population.
The America scenario (segregation, ghettoization, rampant violent crime, erosion of the welfare state due to a lack of solidarity, skyrocketing inequality) is a much more likely long-term scenario than civil war (and almost as disastrous).
Regardless, universal military service is a good means for a bit more social cohesion in a heterogeneous society in order to make sure the America scenario does not materialize, and it is good for young people to become more disciplined and to be able to defend themselves and their country if necessary.
