This is a multi-generational issue.

https://www.newamerica.org/in-depth/terrorism-in-america/who-are-terrorists/
http://www.pewresearch.org/fact-tank/2013/10/15/crime-rises-among-second-generation-immigrants-as-they-assimilate/

The first site is making an argument against Muslim immigration without intending to.  I wonder if Parisians and Londoners felt better knowing that terrorists there have been "homegrown".  We have more than enough people and problems to solve without importing more from low reward and high risk populations.