It's the other way around: the radicals have a need to engage the rest of society to convert them to their cause. That forces some degree of moderation, they kn

It's the other way around: the radicals have a need to engage the rest of society to convert them to their cause. That forces some degree of moderation, they know that if they are too far out no one will listen to them. A better metaphor would be that if you confine the Christians to their ghettoes soon someone will take up arms against the infidels.