The real problem is that Radicalized Christians are NOT a problem. Hopefully, they will become one for freaks like this.
“Radicalized Christians”? Was bedeutet das? (For the folks who do not understand German, “What does that even mean?”)
There have been some sects that have twisted the Christian doctrine into some kind of war code, but they have never had much popularity outside a very small circle, and usually disband after a few months at most, because the leader gets murdered by one or another of his followers.
But for Islam, there is no such internal schism. The entire basis of that ideological scheme is to convert those who do not now subscribe to their vision of the world, or put them into a position of serving as a slave to the converts to the True Belief, or failing to fit into either of those categories, death, preferably by beheading with a long sharp sword of some sort, or in the interests of expediency, a bullet at the base of the skull. Sounds pretty much like Islam has to be on a continuous war footing to assert their supremacy, but then, maybe that is an exaggeration, and it is only necessary for the horde to surround the habitat of the unconverted one at a time.