If there was a war in Heaven before the creation of the world, as the Judeo-Christian tradition implies, then the world often presents us with considerable evidence that the good guys lost.
The recent executions in the offices of Charlie Hebdo did something that news frequently fails to do: shock us. A daily diet of violence has dulled our senses, but this meeting of pen and sword was enough to amaze. Suddenly the clamour of Islamic State's medieval, savage war drums were transported from cave to cafe. For once, we noticed.
We find ourselves in unfamiliar territory. Our society prides itself on tolerance, or at least believes itself to be so, but how far do you tolerate intolerance? It's a question played out in classrooms and playgrounds and corridors.
In schools we try to provide a safe space for young minds to try out ideas, to evolve out of their childish chrysalises into something more complex. Children test out their ideas and their identities. Some of these ideas are unpleasant, and you only have to remember your own childhood to appreciate how brutal teenage "repartee" can be.
The roots of intolerance are buried deep in the soil in which they grow. Stand-up comic Denis Leary used to say, "Racism isn't born, folks, it's taught. I have a two-year-old son. You know what he hates? Naps. End of list." Younger children repeat the cruel dogma of their nursery, repeat what they hear at home, until eventually it becomes part of them. I've heard 11-year-olds call each other the N-word, almost oblivious to its impact and dazed when you clobber them for it. I've spoken to serious, compassionate 18-year-olds who parrot anti-Semitism like it's a nursery rhyme.
The only thing teachers can do is tackle it head-on. On one level, we perform a balancing act that any liberal society must: we enforce public codes of civility; we police the right of expression. On the other side of the tripwire, we regulate and prohibit, admonish and reprimand the overtly discriminatory. We protect two flanks: free speech and the right not to suffer intolerable offence. That's a line as thick and as blurred as coastal fog, but we can still say the fog bank exists. Just because it's fuzzy around the edges doesn't mean there is no boundary.
It's hard: who wants to tell anyone how to think? But as adults that's what we're called upon to do - to draw lines even when we feel uncomfortable with where they start. We provide the scaffold upon which children build their own moral code.
Last week, I used the Charlie Hebdo killings as a catalyst for a class discussion of tolerance, and was quietly proud of what came out of it: sympathy, both with the satirists and with the sensitivities of mainstream Muslims who have been dragged into this artificially polarised debate. It wasn't an easy topic, but teaching children how to navigate the moral reefs of an uncertain world was never going to be easy. It's a task we should never shirk.
Read more about tackling extremism on pages 26-30
Tom Bennett teaches at the Jo Richardson Community School in Essex and is director of the ResearchED conference