Its time to get our heads out of the sand. Religion is part of the problem whether its Islam or Christianity etc. I agree other factors play a role too.
Religion is the best tool to brainwash people.
Right wing extremists don't use religion.
Left wing extremists didn't use religion.
Radicalisation does not need religion.
If religions where purely spiritual and said nothing about the world then I would agree with you, but then I guess there wouldn't be any problems either.
But the claim wasn't religion or things like religion lead to extremism.
It's wrong to say that only religion leads to extremism, and it's even more wrong to say that only Islam leads to radicalisation.
When you recognize that I hope you also recognize that religion is the main cause (or tool) of extremism in the world right now, and that Islam plays the biggest role there.