Most societies have exerted control of individuals they find dangerous by threatening to make the remaining life of a criminal miserable, or to simply confiscate it. This works well enough (with plenty of opportunity to improve existing practices): people with evil intent mostly think they will be caught and punished, or killed in the process of a violent act, and an expected value calculation comes out in favor of not doing the crime.
Sometimes violence isn’t a crime; the civilized world would have applauded the White Rose for blowing Hitler up if they had succeeded, and certainly (if it ever happens) the armed citizen who puts down the lunatic about to shoot up a school or theater is simply doing the right thing. People give up their lives to do good in this world, like the soldier who throws himself on the grenade to save his buddies.
Some very large amount of hideous behavior never occurs because most people have a working moral sense whether or not it derives from religious teaching, and some faiths assert an eternal post-life time during which acts on earth will be punished or rewarded, so doing wrong is discouraged by some combination of just knowing what wrong is, and a selfish benefit-cost calculation.
When religious teaching promises heavenly reward for savagery on earth, we face a distinctive set of challenges (and what seem to be new levels of savagery, like sending a ten-year-old girl into a market with a bomb). Suicidal murderers are not deterred like bank robbers by the fear that they won’t “get away with it”; oversimplifying only a little, they have been sold the belief that the mayhem they are about is a quick ticket to eternal happiness. If their present life is a dead-end struggle in a segregated banlieue slum, so much the better. There is no practical sanction society can threaten such a person with to get a good benefit-cost calculation, especially if the society trying to protect itself looks like a bunch of ungodly infidels. Neither armed guards hoping to shoot first, nor a room full of heat-packing citizens going about their business, offer more than modest protection against a suicide bomber at the security desk or door, or in a large heavy vehicle with a running start. Tactics directed at the bombers and shooters, that kept gangster crime in last century down to a dull roar, are toothless here.
Perhaps we are coming to a time when a particular category of religious doctrine, and merchants thereof, are indigestible to a functioning society, just when the “functioning society” has become something more like “humanity” then “Nation X”. The idea of a country’s “internal affairs” has been shredded by the internet and the 747, and isolation of toxic sources is penetrated by prison gangs and cell phones. The doctrine doesn’t have to be religious, as the direct-action anarchists of the turn of the last century showed, but now it almost exclusively is, and the anarchists were (i) motivated by human welfare on earth, not pie in the sky when we die (ii) a lot more concerned to blow up and shoot political leaders, who can be practically protected, than dozens and hundreds of ordinary citizens.
In addition to the invocation of unprovable, unarguable theology to justify savagery, the current breed of terrorists share another brand of villainy with (for example) kidnappers, by turning our best instincts, like due process of law and respect for life, against us.
Back in the day, there was a status of “outlaw” that malefactors could earn by doing a lot of really bad things and refusing to submit themselves to the courts. An outlaw so designated was denied the protection of the laws and could be legally killed by anyone who got the drop on him. I am not much troubled by the extremely rare criers of fire in crowded theaters, but the lunatic fringe of radical Islam, that breeds suicidal terrorists by a supernatural reward proposition not susceptible of assessment with facts or evidence, is starting to make a concept of freedom of speech that has served western society well for a long time look oversimple. Egging on lost souls to shoot abortion providers, while staying safe and cozy in front of a computer, is a similar category of criminality, but its death toll and even its total toll of human suffering is manageable (could be better, of course) by our usual criminal justice tools and informal social controls.
ISIS, Al Qaeda, Boko Haram, and the lot are a different problem. The generals very likely believe for themselves the eternal reward story they peddle, and drone strikes on them have not exactly shut down the machine. It would be better if the civilized world didn’t give them Abu Ghreib, Islamophobic bigots on Fox News and talk radio, Marine le Pen and all the other excuses to view us as deserving extermination, but they are not fighting a war for fair treatment by oppressors. They are fighting a war to reverse thirteen centuries of human development and using every piece of that development they can get their hands on, from gunpowder to electronics to habeas corpus, to do it. They are not a criminal justice problem, nor a military problem, nor a social justice problem; they are something new (at least in the last few centuries), different, and strategically deeply perplexing.