There is, so some people claim, a tension or even contradiction between fighting terrorism and protecting our civil liberties. As the Daily Express put it, “It is absurd and dangerous to apply Queensbury rules to measures taken by the authorities … all that matters is success” – though they published that, not in response to any our recent terrorist outrages, but in the 1970s in response to the IRA’s bombings.

These words could however, so easily have been written recently. But have we really learnt so little since the 1970s?

For the reality is that the attitude of “we must get the evil-doers at all costs” resulted, in case after case, in evidence forged to suit and innocent people being fitted up. And when you jail the innocent you not only punish them wrongly, but it means you let the guilty off scot-free and your injustices make it easier for the terrorists to recruit support for their cause.

And one of the things terrorists want is to get rid of liberal society. It’s their enemy. So stripping away our freedoms is not fighting them – it is doing what they want.

And stripping away our freedoms, with ID cards and DNA databases, means pouring resources into keeping track of innocent people rather than tackling terrorists.

What would you rather millions of pounds and thousands of people were poured into? Looking for terrorists? Or keeping tabs on the innocent?

But we also need to recognise that simply saying “terrorists are evil, their acts are inexcusable” doesn’t help understand where their support comes from – and without that understanding, the sources of its support cannot be tacked.

The problem so often is that, yes – terrorists are evil, but no – not everyone who helps them is so irredeemable that we can’t imagine plausible circumstances under which they would not have helped. Especially when we remember that “help” often includes behaviour such as turning a blind eye to what someone who knows someone who lives next to someone else is up to.

Understanding what motivates people to turn a helping hand or to turn a blind eye is what is needed to cut the ground from under terrorists and make it harder for them to operate.

So, no – I don’t think any amount of alienation, poverty, discrimination or exclusion excuses murder, and I’m doubtful how many fewer terrorists murderers there would be if all those were tackled (after all, those in the UK in recent times have been rather more middle class) – but I am sure that those same terrorist murderers find it easier to operate when they are surrounded by people who do suffer from alienation, from poverty and from discrimination.

So let’s stop spending millions on tracking the innocent and focus our efforts on tackling the causes of terrorism and catching and disrupting terrorists!