How does one spot a radical? It takes one to know one. But not really.
A radical is someone who does not conform to the mob (culture) of origin belief system.
So what would someone growing up in a society that believes in and promotes the belief in a supernatural force know about realty? Would it not be better to inoculate the population against belief in a supernatural force and get on with life, a life with a common purpose, the betterment of all humans, not just advancement of your chosen group?
After you spot a non-believer, what are you going to do with him? Execution? Well that would be a bit extreme? Jail him for his beliefs? Retrain him? But what about philosophy? Totally radical, yet tending toward the truth... a better system that exists among the religions (belief systems based on supernatural or old book, tradition). Many of them believe, even live, the StarTreck Prime Directive - Do not interfere in other cultures, in conflicts. They can believe what ever shit turns their crank. But if they bother us, we will beat the shit out of them. Reworded for sure.
And if you chose retrain him, retrain him to what? Take a person such as I are, (just for you english police). We know there are four stages of time: Past, present, future, and never-never. Which one are you thinking in and which are you living in? How high do you value human life - yours, and others lives? Is a belief system worth dieing over? Cato, Socrates, Seneca, Zeno and others said it was. Others learned to endure, and hold true to their knowledge system. When does a belief system become knowledge system; when the truth is known.
The obvious choice is to exclude or shun the proven radicals. Tag all those who head to conflict zones and transfer point to conflict zones. One way passage only out of the country. Exit visa required for everyone. Anyone who cannot prove there whereabouts during there absence cannot come back. This makes participation in foreign affairs without government approval a life sentence. This could be extended to the families, producing consequences on those who help raise radicals. Start a report the radical program? But how does one define a radical before they take action? Thoughts and beliefs are not enough and they can change.