I would assume that Holland like most countries has ways of revoking the citizenship of persons that violate the law.
In the United States a naturalized citizen can have his citizenship revoked if he is convicted of a felony.
The same is true also of my native country Argentina. I would assume most countries have such laws on the books.
I don't know for sure. But a few weeks back another imam was let off the hook when he made remarks about homosexuals. He claimed he could say it, because of the freedom of religion. The judge agreed and he didn't have to pay a fine like a priest who said almost the same.
You see, islamists are protected by law and the apologists will do everything to protect them.
Before they could be punished in any way, there is a long way to go.