In the early thirteenth century, the Catholic Church responded to the gnostic Cathar heresy by initiating the Albigensian Crusade, one of the most violent episodes of medieval religious suppression. It's the origin of the saying "Kill them all, God will know his own" as well as the reason you don't run into many gnostics these days.
Today, Abdul Rahman was granted asylum in Italy following his near execution under Sharia for having converted away from Islam.
This approach to buttressing a religion has always struck me as demonstrating either a stark pragmatism or a distinct lack of confidence in that religion. Either you don't honestly believe in the truth of your religion and have concluded that you really do need to kill people to keep them from leaving, or you are afraid that your faith isn't as strong as you think...and come to the same conclusion.
There is, of course, option number three. The faith is nothing to you, but you understand that having a unified religion -- and a group that fanatically enforces that unity -- gives you power over people.
Faith is secondary.
The thirteenth century is still going strong all around the world.