I and others who supported the invasion of Iraq a decade ago did so because we thought that Saddam Hussein’s regime was among the worst in the world. This was, on the one hand, because of his propensity to violence against his neighbours – Iran during the 1980-88 war and Kuwait, which he attempted to annex in 1990 – and, on the other, because of his eager sponsorship of terrorist groups that saw the destruction of Israel as their life’s (and death’s) work, as did he.

But more significant still was the active delight in savagery in which he indulged, and passed on to his sons and presumed heirs. This he visited on the Kurds, on the southern marsh Arabs and on those, including members of his entourage, whom he suspected of disloyalty or who were linked to supposed traitors. It was a savagery which, unlike that of his hero Stalin, was not governed by a great deal of rational calculation: Saddam’s war against Iran was a disaster for his nation and the invasion of Kuwait still more so. The possibility that such a man might possess weapons of mass destruction was a nightmare for the world.

In the event, it seemed he did not possess, or no longer possessed, the weapons he either had once had, or desired and planned to have again once the sanctions regime loosened, as he reckoned it sooner or later would – a reasonable calculation, incidentally. The US and UK intelligence services believed he did have WMDs, as did all the other states with large foreign intelligence capabilities. According to some accounts, Saddam believed it, too, misled by aides who were afraid to tell him that the weapons had been destroyed. They were all wrong.

Two reports – by the UK’s Butler review of July 2004 (led by Lord Butler, a former cabinet secretary) and by the US Commission on the Intelligence Capabilities of the United States Regarding Weapons of Mass Destruction in March the following year – found that the respective intelligence agencies had made grave errors. The US commission was the harsher of the two, characterising the mistakes as cumulatively “one of the most public – and most damaging – intelligence failures in recent American history . . . in large part the result of analytical shortcomings; intelligence analysts were too wedded to their assumptions about Saddam’s intentions”.

The Butler report was more restrained, but also pointed to weaknesses in MI6’s checking of sources, a reliance on third- or fourth-hand sources and on dissidents, a surprising neglect of thorough information-checking in the prelude to the invasion by security officials and ministers alike, and, in particular, the weakness of the claim that Iraq could fire off rockets containing WMDs within 45 minutes – for which there was a source, but a highly dubious one.

However, Butler also concluded that Iraq was actively seeking WMDs, including the development of a nuclear weapons programme, before the invasion; that it was developing ballistic missiles with a longer range than permitted; and that the claim that it was trying to import uranium from Niger was credible, as was another that it was trying to buy mobile biological weapons labs.

Neither the UK nor the US reports was the last word; no last word will ever be said, though the report of the Chilcot inquiry, more comprehensive than that of Butler and expected to run to a million words, is now scheduled for publication towards the end of this year. There is some crucial material that is still classified – including notes between the then British prime minister, Tony Blair, and the US president George W Bush.

Nonetheless, I maintain that an adequate summary of the position now is that Bush determined to attack Iraq because he believed, on some false premises and some sound ones, that it was an active regional and even global threat. Blair supported Bush because he believed the same, though he put more stress, both in private and in public, on the moral case for intervention, holding to the thesis that states have a “responsibility to protect” their citizens which, once flouted grossly and over time, is a prompt for external intervention. The doctrine of the “responsibility to protect” was then (and is still) a subject of much discussion at the United Nations. There was nothing resembling a consensus around it, and there will not be one any time soon, at least as long as powerful nations such as China and Russia regard it as being against their interests and while others, notably Germany and France, see it as being, at best, a very occasional duty.

Opponents of the war in Iraq, whom I would guess are in the large majority in Europe and the US, often point to a wide spectrum of reasons for the invasion beyond the ones officially proclaimed. These include: the US’s desire to secure oil supplies; its wish to demonstrate in the harshest possible fashion its global dominance; revenge on the part of George W Bush for the attempted assassination by Iraqi agents of his father, the former president George H W Bush; Blair’s willingness to be an obedient lackey of Washington in the hope that Britain might get a share of the oil and other loot to be expected from an invasion; and his self-image as a global superhero, righting wrongs across the world. In many countries, especially in the Arab world but also in Europe, the invasion is seen as proof of Jewish control of finance, politics and the media, as well as Jewish sponsorship of the attacks on the Twin Towers and the Pentagon on 11 September 2001 in order to create a casus belli.

Much attention has focused on two issues: the falsity of the claim that Iraq possessed stocks of WMDs, with the suspicion, often amounting to certainty, that the intelligence was manipulated to show what Bush and Blair wanted it to show; and, in the UK, the belief that Blair had agreed with Bush to support the invasion long before he announced that the UK would participate, and also before parliament and the cabinet had agreed, as both did. Indeed, at least in the UK, these two issues usually drown out all others, especially on the left.

Experience over the past decade has shown that argument over these produces nothing but mutual incomprehension. For the record, I believe that: a) both the US and the UK governments accepted intelligence that pointed to Iraqi possession of WMDs, but interpreted it in the way most favourable to the case for invasion and b) that Blair wished to support the US largely because he had long thought Saddam a major threat (though he had failed to convince the former president Bill Clinton, who also believed that Iraq had WMDs, to take action), but he insisted that Bush take his invasion plan to the UN before giving Britain’s formal agreement.

In the immediate aftermath of the invasion, attitudes on the British left hardened quickly into a self-satisfied conviction that opposition was justified, together with the belief in many quarters that the UK’s involvement in Iraq was emblematic of a New Labour administration that was mendacious, servile to the US and scornful of the UN, the European Union and the rest of the “international community”. This was, and still is, the view of many senior officials. The attitude entailed – not everywhere, it ought to be said – a deliberate blindness to the dangers of a Saddam-led Iraq and to the clear danger that his determination to become a WMD-armed state would pose. There was blindness, too, to the American and British containment of Iraq, with almost no support from other European states by means of a no-fly zone over Kurdish areas. And little attention was paid to the failure of the French, the Russians (who led the opposition to the invasion), the Germans and any other Europeans to develop what the American political philosopher Michael Walzer has called the “little war” alternative to the “big war” by the US and the UK – a little war that would have tightened the sanctions regime to the point where Saddam might have been required to change his behaviour.

There was some left-wing support for the post-invasion reconstruction of Iraq, which came mainly from elements in the British trade unions, rallied in large part by the tireless work of Abdullah Muhsin, an official of the students’ union in Iraq who had been forced to emigrate, and aided by the parliamentary researcher Gary Kent. Muhsin, Kent and others put before the left in this country the facts of the suppression of trade unions and workers’ movements, as well as calling for the occupying forces to leave Iraq and hand over power to democratic parties. The support came in the form of a handful of conference resolutions and a few visits to Iraq in solidarity (I went on one, as a journalist), but it had little practical effect.

There has also been a wilful blindness to the passivity of the EU on this and other security matters – something that is becoming more salient as the US furls its global security umbrella and concentrates on developing a relationship with China. Europe has not and probably will not (at least not soon) develop anything like a common security and defence policy. Strategic thinking is required, therefore, especially on the part of the major states, about how Europe could operate as a loose gathering of countries to promote peace and freedom beyond its borders. Unfortunately, much of the left’s rhetoric has remained on the level of blame – for the US, New Labour and Israel – with little engagement with the threats, and possibilities, of the world as it is now.

Those of us who were for the invasion may still be “right” – right, that is, on the kind of timescale assumed in Zhou Enlai’s supposed remark to Henry Kissinger in 1971 to the effect that it was “too soon to tell” what the consequences were of the French Revolution two centuries earlier. (It now seems likely that Zhou was referring to the 1968 students’ revolt in Paris, but, as a US diplomat present at the conversation said, the misunderstanding was “too delicious to invite correction”.) It cannot be known what would have happened if Saddam had remained in power: my guess is that sanctions would have decayed and that relatively soon there would have been a WMD-armed Iraq, just as there is likely to be a nuclear-armed Iran and already is a nuclear-armed North Korea.

Rightly or wrongly, we were too sanguine about the prospects of regime change, especially in the light of the mess made of it. This was perhaps inevitable, because even well-trained armies are good at destroying but not fitted for constructing. In my case, nearly a decade of reporting in central and eastern Europe and the former Soviet Union for the Financial Times predisposed me to see western intervention (not military in that instance) as benign, as I believe it generally was. But we did not anticipate that Iraqi forces who hated the US – including those loyal to Saddam – would dominate after the invasion, that the population would not be active in ensuring democratic choice as it had been in, say, Poland, and that the west had limited staying power. We were much influenced by Kanan Makiya’s searing book Cruelty and Silence (1993), which detailed the horrors of Iraq under Saddam and called for intervention – an intervention, the author argued, that would be greeted with “sweets and flowers”.

However, the responsibility to protect remains a powerful moral imperative. It must remain part of the armoury of those states with the power and the will to stop tyranny where it is possible to do so and where intervention is likely to work – as it did in Sierra Leone, in Kosovo and ultimately in Bosnia. It may work in Mali. More thought needs to be given to how it might work in Syria. For the left, the responsibility to protect should be part of a progressive view of global problems. That the principle has become synonymous with a kind of refurbished imperialism is a sign of decadence.

John Lloyd is a contributing editor of the Financial Times and a former editor of the New Statesman