This paragraph jumped out at me because of the numbers involved:
"Starting in 2012, 34 people went from Aarhus to Syria. As far as the police know, six were killed and 10 are still over there. Of the 18 who came back home, all showed up in Aarslev and Link's office, as did hundreds of other potential radicals in Aarhus — about 330 in total."
If a small town like Aarhus harboured 34 people that joined ISIS and 330 potential radicals in total that does not bode well for the rest of Western Europe.
Those numbers, when extrapolated make the problem a lot larger than I thought it was (and I actually thought I was over-estimating).
Aarhus has a population of only ~320K, so that's 1:1000.