Born in France doesn't mean socially and culturally integrated. Many of these attackers were children of immigrants who either didn't integrate because of their own cultural beliefs or because the host society didn't provide the necessary conditions. Whatever the reason, these people didn't feel like they belong to the host societies and radicalized. If anything, these attacks are examples of unsuccessful integration and of the failures of free movement and immigration of people of radically different cultural beliefs, and not the other way around.