Johann Hari: It may please many Iraqis, but it's still wrong

It is, on this subject, my first sliver of doubt. Seeing a rope placed around Saddam Hussein's neck - and hearing the ecstasy of my friends in Baghdad, saying this is a sweet, lingering moment of justice - has forced me, for the first time, to wonder if I really do oppose the death penalty at all times and in all places.

This is a strange jolt. For me, opposition to hanging has always been manifestly moral. Should the state take a defenceless, unarmed prisoner and break their neck? Obviously not. It is a sign of civilisation that you treat even the most depraved and despicable people with decency. And yet - I have to admit it - when I saw Saddam's snapped corpse, I was pleased.

I spent some time in "his" Iraq. I saw the raw terror at the mention of his name. I saw the Marsh Arabs rotting in rusting desert huts after Saddam poisoned their marshes and slaughtered their families for the "crime" of calling for democracy. So when my friend Ahmed - whose father was murdered by Saddam's goons - said in a 4am phone call that he felt his dad was finally at rest now, the anti-death penalty arguments died on my tongue.

So should there be an exception for tyrants, the Mussolinis and Caecescus? This question forced me to go back to first principles. I do not believe in killing people to meet some abstract, quasi-religious standard of "justice", where a death must be avenged with a death. No: the only justification for using violence, ever, is a utilitarian one - to prevent even more violence occurring. To choose the least controversial example, innocent people died horrifically in the bombing of Nazi Berlin - but even more people would have died if the bombing had not gone ahead, so it was not only justified but morally necessary.

(I thought, along with a majority of Iraqis, that the invasion of Iraq was justified by a similar utilitarian calculus. We were wrong: more than 650,000 have now died, compared with 210,000 if Saddam had continued murdering at the same pace. I should have known better - plenty of others did.)

Of course, the defenders of hanging, the gas chamber and the electric chair as tools of everyday democratic government use precisely this utilitarian argument. They say killing murderers deters other people from following their path. But the evidence shows they are wrong: Oklahoma state, for example, has had consistent murder rates before, during and after a recent 25-year moratorium on capital punishment.

It doesn't deter dictators either. Is Kim Jong-Il or King Abdullah of Saudi Arabia going to torture one person fewer today? Of course not. Yet when dispensing with ex-dictators, there is an additional consideration. Executing them ends the perpetual fear among the population of a restoration. While it is nonsense to say this will break the back of the Baathist wing of the insurgency, nobody in Iraq today fears - as they truly, madly, deeply did two days ago - that there will come a time when Saddam is back and they will be made to pay for supporting his opponents. (Of course, they have plenty more to be terrified of: more than 1,000 people are dying every week in Baghdad alone).

But is this enough? Does the relief and joy given to a once-tyrannised population outweigh the murder of a human being? No. In the end, I cannot find a morally justifiable explanation for my glee at Saddam's death. The real test of your belief in human rights is not whether you support them for the innocent - the Marsh Arabs and the Ang Sang Suu Kyis. No: it is whether you support them for the disgusting, the depraved, the genocidal - the Saddams. Today, Iraqis have achieved one sort of victory over their tyrant. But the greater victory would have been to say - you hanged; you tortured; you butchered; but we will not do that. We are better than you.

But how do I suggest that to Ahmed, who is enjoying his first happy day in a year? How can we lecture Iraqis on anything, when - in infinitely easier circumstances - we have failed to deal with our own Iraqi-killing criminals? To give just one example: in November 2004, the US forces, with logistical support from the UK, surrounded Fallujah - a civilian city the size of Leicester - and forbade males between the ages of 18 and 60 from leaving. They then released a chemical weapon on the city's residents - white phosphorous - that burns flesh right down to the bone. There is no utilitarian justification for this; it is a vicious war crime. Somebody - Donald Rumsfeld? George W Bush? - ordered it, just as they have ordered the use of torture and secret prisons across Iraq.

Once they have been punished, I will feel able to tell my terrified, terrorised Iraqi friends that this weekend they failed to defend human rights as they should.

j.hari@independent.co.uk