Assimilation in France Research

http://www.migrationinformation.org/feature/display.cfm?ID=165 - Assimilation Policy

This policy from the French Government outlines that legal immigrants must sign an integration contract. This contract states that legal immigrants must accept the French values of society, these values being accepted and undertaken with the immigrant being granted a 10 year residence permit. If these values aren't accepted, the immigrant is only given a 1 year permit to stay in France. 

"By spreading these values among foreigners living on French soil", Fillon said, "the government wants to combat the threat of dissolution into culturally distinct communities that would threaten France's national identity."

The secondary purpose of the law bears directly on integration by extending the time required for aliens who have a temporary permit to obtain a long-term residence card. In addition, in order to obtain the card, immigrants must provide proof of their "integration into French society." 

These quotes from the article above show that immigrants must adapt accept the values of French society in order to be part of it. The government stating this policy connotes that everyone is the same, and if you're not, you're not accepted in French society and you may be seen as a threat. This is what the main characters of La Haine feel.