I listened on Saturday morning to BBC Radio 4’s phone-in programme, Any Answers, which was dominated by the horrifying events in Paris on Friday evening. Amongst the dozen or so who called in to air their views there were the usual cranks, including a man advocating the incarceration of the families of terrorists, and suspected terrorists, in concentration camps, but the majority of the despair was liberal and thoughtful.

A British man called from Paris first to commiserate, and then to make the point that Paris is a much less contentedly multiracial city than London. Its North African Muslims, particularly, feel marginalised and excluded, and large numbers live separately in what amount to suburban ghettos. They have fewer opportunities, and are often subject to open discrimination. Many are angry, resentful, frustrated, and, as a consequence, they may be prey to religious radicalisation. He made these points reasonably, and was equally as angry about Friday’s atrocities and as sorrowful as any of the other callers. He mentioned that he is of mixed race himself, and was always more conscious of this in Paris than in the UK.

The caller who followed him was indignant, suggesting that his predecessor had been ‘excusing’ terrorism by attempting to explain it. This was before the identity of any of the killers was known (at least one, it now seems, was a radicalised French Muslim), and before IS claimed responsibility.

I remember many years ago the outrage that followed a remark made by Cherie Blair, wife of Britain’s former Prime Minister. She let slip that she ‘understood’ the frustration of the Palestinians who carried out attacks against Israel. She was forced to retract and apologise, though she never meant to excuse Palestinian terrorism.

But to attempt to understand and to explain is not to excuse. Understanding is essential if there is to be solution and prevention. Of course nothing can excuse the cold-blooded killing of non-combatant civilians going about their everyday lives in the streets, cafes, stadiums and concert halls of Paris, except perhaps insanity (and perhaps insanity doesn’t excuse, even if it negates legal responsibility). Whatever our background, unless we are certifiably insane, we choose what we do and are responsible for our actions. Just as we do not discount the merit of courage if a brave man or woman has been lucky in his or her family and education, so we do not discount evil if it’s perpetrated by the marginalised, the unlucky, the poor.

After all, if explanation were a form of excuse, then we could all blame our actions on the interactions of our cerebral synapses, which we don’t control at the cellular level. As conscious, sane, adequately intelligent, adult human beings we are responsible for what we do however we are formed.

But nevertheless it would be stupid to pretend that policy doesn’t affect the conditions in which wrong choices are made. Following the riots of Britain in 1981 when the disaffected and recession-hit communities of Brixton and other inner cities flung Molotov cocktails at the police, the Government commissioned a public inquiry which found evidence of racism in police behaviour towards the black community. Legislation and a massive programme of investment followed, despite Margaret Thatcher’s refusal to accept communal disadvantage as any kind of explanation.

It would be stupid, also, to suppose that ‘Western’ policy in the Middle East hasn’t had a causal influence on what’s happening now, though it isn’t at all obvious what anyone should do next. Poverty and contempt breed violence.

Explanation and understanding are essential, alongside emotion. Concentration camps, bombing, and walls, solve nothing in the long term. But, even so, nothing excuses individual acts of terror and murder. I am sorry for all those affected by Friday’s events in Paris. What must we do to prevent further tragedies?

Even if Paris doesn’t always live up to the high ideals of Liberty, Equality and Fraternity, they are strikingly less prevalent in the Middle East, from where most of today’s terrorism comes. Whether that is because of, or despite, the West’s century or more or meddling, is a larger topic. One way or another there are precious few benign regimes in the region, and even fewer that are liberally democratic. Everyone seems to know that the solution lies there, but no one knows what it is.