... rising popularity of Islam among Europeans is a huge challenge to European security?
First of all, the pilot was dx as bipolar, as of last report . It was also noted in the Press, that the pilot was being medicated for his medical problems.
There are many converts to Islam and most are neither depressed or bipolar individuals. Likewise, conversion to the religion of Islam does not "cause" an individual to become radical. If it does, than how do you account for the millions of peaceful Muslims on this Earth?