Animal rights extremists don't use religion.

Right wing extremists don't use religion.

Left wing extremists didn't use religion.

Radicalisation does not need religion.

All of those are ideologies with certain views on how the world is and how it should be, which can also said of religions.

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.

Sure, they're like religion.

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.

Nobody is saying only religion leads to extremism.

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.

Religion is among the best tools to brainwash people then. If something really makes sense, you don't need people to believe it blindly.