The urge of much of Britain's political establishment to attack Syria is in retreat. The prime minister's eagerness to join an American bombing run on Damascus hit a humiliating reverse in the Commons on Thursday evening. The prime minister now appears to accept there will be no British intervention in Syria.

Prior to the vote, Downing Street had been swerving and skidding to avoid the Iraq trap. It wisely published the intelligence report indicating the Assad regime used chemical weapons in a raid on a Damascus suburb, possibly in random retaliation for an attempt on his life. Such weapons are illegal under international law. While it was wrong to rush to judgment with inquiries still in train, there is justice in a desire to enforce the law. But enforcement must be meticulous in its legality. Otherwise what is dispensed is anarchy, not law.

The government claimed it could attack Syria under the UN's "responsibility to protect" doctrine, where people in a foreign state are abused by their own government. We know from the Iraq invasion that British politicians are adept at finding lawyers to say what they want. But facts are facts. The UN's resolution 1674 on responsibility to protect plainly states that such action must be "through the security council in accordance with the charter". That process was absent.

The use of chemical weapons is awful. But to treat their apparently random use to justify an urgent, extra-legal attack on a foreign state is wilful. It had been precipitated by President Obama's unwise warning in the summer that such use would cross a "red line". This is odd from a leader whose own arsenal embraces phosphorous and depleted uranium shells and delayed-action cluster bombs, not to mention nuclear weapons. Why such dreadful weapons are not taboo, and chemical ones are, is a mystery.

Obama's intention is currently for a "limited, tailored … clear, decisive shot across the bows" of the Syrian government. The tactical basis for this is obscure. It can hardly claim to deter a chemical attack, since the red line speech tried and failed in that respect. While Assad seems unlikely to repeat the outrage, the idea that he will roll over if bombed and stop killing his people is naive. As for "degrading" his arsenals, if this releases chemical clouds how stupid is that?

The likelihood is now of a single burst of destruction by US forces if only and blood-letting, to assuage the do-something lobby. This can hardly alter the balance in the civil war, though it seems certain to increase the refugee flow, alienate Russia and its regional allies, and infuriate a newly moderate Iran. All this is to "punish a dictator" in what seems depressingly like a gesture to allow western politicians to strut tall and feel good.

Something-must-be-done wars have a long and wretched history, notably in the Middle East. It was after Ronald Reagan saw television footage of the Sabra and Shatila massacres in 1982 that he ordered his marines into Beirut. He later withdrew them, leaving 265 American dead and Lebanon with a further decade of ghastly civil conflict.

In 1986, the US tried to kill Libya's Colonel Gaddafi over a terrorist attack in Berlin, merely ensuring a further burst of Gaddafi-sponsored terrorism. In Kosovo in 1999, the Nato bombing of Belgrade did nothing to impede ethnic cleansing, indeed it probably expedited it. What tipped the Russians into forcing Serbia to back down was the threat of a western land invasion.

In 1993, President Clinton bombed Baghdad in retaliation for a claimed plot to kill former president George H Bush. This was followed five years later by the further bombing of Iraq in Operation Desert Fox, this time to deflect attention from the Monica Lewinsky affair. Its declared purpose of eliminating weapons of mass destruction was so botched as to require more bombing and the eventual invasion in 2003. Then as now, the zest for aggression seemed driven as much by the military-industrial complex as by legality or evidence.

Overstating the military and political potency of air power – mostly as a "sending of messages" – is as old as air war itself. Tactical bombing is occasionally effective where, as in Libya and initially in Afghanistan, it is in close support of ground forces. When, as now, it is intended as a soft option to ground action, it merely destroys.

The one sound strategic reason for intervening in Syria would be to topple President Assad. Cameron was unable to tell the Commons how raining bombs on Damascus contributed to this perhaps as advice was that this might be illegal. The idea that a region afflicted by decades of sectarian conflict will be driven to peace and democracy by a few Tomahawk missiles is absurd. And who was it that Cameron wanted to see take over? Hezbollah or a new (and probably no less brutal) Sunni supremacy?

The desire to re-order foreign states – still embedded in parts of the British establishment – has long been subsumed in the constitution of the UN and international courts of justice. These may seem imperfect, but they are how the world has agreed to legitimise actions that infringe the integrity of independent independent countries. When Britain went to war in Kuwait, the Falklands and Libya, it did so with proper UN legal cover.

The Syrian civil war is awful to witness but not exceptional. The Lebanese civil war next door claimed 120,000 lives and created millions of refugees. The Iraq war, a similar sectarian conflict, claimed even more lives and continues to do so.

Sometimes it takes courage to conclude of foreign conflicts that we can only do more harm than good by meddling in them. But the idea that not meddling constitutes "allowing them" to continue is a short route to madness. The logic of most civil wars is that they end either when the combatants fight each other to exhaustion, or when some neighbouring power invades and quashes them. Dropping a few bombs would have been the nearest the British government got to Cameron's own charge of "standing idly by". It would have been careless of outcome, halfhearted intervention, intervention-lite.

In Syria the human misery is intense and agonising to watch. It merits extremes of diplomatic engagement and humanitarian relief, to which outside attention and expense should surely be directed. Bombs are irrelevant. They make a bang and hit a headline. They puff up the political chest and dust their advocates in glory. They are the dumbest manifestation of modern politics.