My current doctor is an Iranian. I imagine he is a Muslim.
Perhaps he is , perhaps not, this is only pertinent if he is sympathetic to IS.
If he has been in the US a long time as a successful doctor , this seems unlikely.
There are estimates that only 10% of Muslims are prone to extremism, Other estimates are even less. I would bet on the lower numbers.
But in the absence of reliable surveys these are just guesses.
Supposing only 3% are liable to join actively , we are still talking about more persons than inhabit Germany. Persons spread across the globe and mixed in with less guilty and innocent persons.
It isn't likely that we could wipe the pool of potential recruits out without causing their replacement among the survivors.
But , we could make an impression on them that leaves them thinking the idea is a bad one.
And -Or , allow them to congregate on a bit of flypaper.