The political debate on Syria has produced a bewildering array of people proceeding from the same premises to opposite conclusions and from different premises to the same conclusions. We have an ‘anti-war’ coalition which unites Nigel Farage, David Davis, Jeremy Corbyn, the SNP, the Greens and the Mail and the ‘pro-war’ camp includes the Tory government, a sizeable chunk of the parliamentary Labour Party, the Liberal Democrats, the Financial Times and the Indy.

At recent party events I have attended there is disquiet and confusion. I see that two thirds of Lib Dem Voice readers oppose the British air strikes. Veterans of Iraq war marches ask why we are not marching again to recapture one of the party’s finest hours. I share some of the confusion no longer having the benefit of participating in discussions amongst parliamentary colleagues. I have had the benefit of Cabinet-level briefings, which led me to endorse air strikes 18 months ago; but much has changed since.

It would be useful to identify a series of propositions on which I believe most reasonable people, on either side of the debate, can agree.

The first is that we are dealing with a conflict of great complexity with a constantly shifting balance of forces and alliances and numerous ethnic, confessional and ideological factions. The enemy is a hydra-headed organisation which pops up in numerous locations, is now well embedded in Libya, Yemen and sub-Saharan Africa as well as Iraq and Syria and has the capacity to mutate indefinitely. The concept of ‘victory’ as employed in the Second World War or the Falklands is almost certainly unachievable and is largely meaningless. We must beware of armchair generals, geopolitical strategists and politicians trying to render this complexity into a simple narrative: a Clash of Civilisations (ie Christianity versus Islam), a Fight against Fascism, a War on Terror.

A second point is that there is much evil on all sides. I buy the argument that Daesh (as we have been told to call it) is exceptionally evil because of its systematic cruelty. But it has fierce competition from the Assad regime, which has killed far more people, used chemical weapons against its own citizens and, like its former Baathist neighbour in Iraq, has practised barbaric cruelty in its prisons. Then there are the various factions operating under the Al Quaeda franchise (which has somehow acquired the label ‘moderate’ in this war) and the Shia militia imported from Lebanon and Iraq.. This is also a proxy war which has attracted in a range of unsavoury regimes –Russia, Saudi Arabia, Iran-all now, theoretically aligned against Daesh. There aren’t too many ‘good guys’, though the Kurds are being lionised in the West even if not by their neighbours.

With so much complexity and confusion, the public debate should be characterised by humility and open-mindedness. That is what makes so unforgivable the crude and abusive campaigning. There is no room in civilised discourse for the Internet trolls and the thuggish activists threatening MPs who voted for air strikes or accusing them of murdering babies. No less disreputable is the attempt by David Cameron to smear those who oppose strikes, even in his own party, as “terrorist sympathisers”. Shrill self-righteousness is a poor substitute for the moral high ground.

We should be able to agree that there are serious risks both to intervening and not intervening. It is simply implausible to believe that air strikes in Syria will make us safer, since there is bound to be retaliation, however clever the security services are in intercepting bombers. But it is equally implausible that Britain can insulate itself from terrorist attacks by abstaining. We are already being attacked as the tourist victims of bombings in Tunisia know to their cost. And the involvement of British jihadis in the fighting means that as a country we are embroiled whether we like it or not.

We should also be able to agree that the British contribution to the military effort, while doubtless of some value, is marginal. The Americans provide the planes, the weapons and the technology. We are not offering ‘boots on the ground’ which might make a difference but is inconceivable after Iraq and Afganistan. In so far as a non-military person can judge, there is already an adequate supply of bombs and planes, which we are offering, relative to targets which are militarily relevant but do not put numerous civilians at risk. It seems self-evidently sensible to attack oil installations which help to finance the Islamic State and makes one wonder why no one thought of this before (or why the refinery is being left alone). In any event, whether the British intervention is right or wrong will make little difference to the outcome of the war.

So, what should the sceptic do who is unimpressed by simplistic and emotive calls to arms or to militant pacifism? It is very tempting to say ‘no’ and to say it is all a terrible mess which we should try to steer clear of. Having voted against the Iraq War, with my Lib Dem colleagues, I can see worrying parallels in the lack of strategic clarity and the potential for blundering into a Middle Eastern swamp with no obvious exit. I find that most of my friends and party supporters assume that my party would automatically repeat its opposition.

But there are some big differences from the Iraq war. There is no question, here, of defying international law. This is not about regime change (indeed we are now de facto allies of the awful Assad regime). Saddam, however odious, was not attacking us. And we are not on the coat tails of a crass, ideologically driven, US administration. On the contrary, the Obama administration has shown admirable restraint and a marked reluctance to extend its military role.

One of the most regrettable features of the Iraq war is that it drove a large wedge between the UK and US on the one hand and, on the other, France and Germany. On this occasion we are with our European neighbours and allies. We are making a statement of solidarity with France, not just over recent terrorist attacks, but in the political battle to neutralise the anti-Islamic hatred being fomented on the Right. We are also with Germany whose government has, at some political risk, courageously embraced Syrian refugees, in marked contrast to our own. Tim Farron is quite right to link the refugee issue with the military conflict and to clearly differentiate us from the Tories. At a time when the European project is in serious trouble, Britain should be part of a common European response of which the air strikes should be just one part.

* Sir Vince Cable is MP for Twickenham and was leader of the Liberal Democrats from 2017 until 2019.