Any reasonable person must accept that Syria's rulers used chemical weapons last month in the outskirts of Damascus. All weapons are awful. The west condoned their use by Saddam Hussein in Iraq and itself has deployed napalm and white phosphorous. But sarin is specifically illegal in international law and Barack Obama told Syria not to use it. Is his word to mean nothing?

The American secretary of state, John Kerry, is in London today pleading that international law must be enforced. We can agree with him. In Cambodia, Rwanda, Liberia and the former Yugoslavia those convicted of war crimes have been brought before international courts. America has rarely been a supporter of such courts, fearing that its frequent aggression against other states might make it vulnerable to litigation. If America is now changing its tune to the relentless enforcement of international law, that is welcome.

But Washington is not talking about bringing Syria's president Assad to account. It does not talk of one day bringing him to justice. It merely wants to bomb his cities in what appears a furious retaliation for Assad having embarrassed Obama by snubbing his "red line" warning. At this point international law is confused with American pride.

Missiles are poor law enforcers. They rarely kill the right people. They cause vast destruction, wrecking the lives of civilians and increasing their dependency on their oppressors. Missile attacks are mere displays of power, usually as a spectacular alternative to a ground assault. Their military ineffectiveness makes them susceptible to mission creep.

Already Obama has shifted from threatening a "surgical punitive strike" to a massively destructive one, intended to aid the insurgency and thus assist in regime change. This happens to be against international law. More to the point, such missile attacks did not "work" in Serbia, Iraq or Afghanistan. They merely served as a prelude to chaos on the ground and pressure for ground intervention.

If Obama means to achieve regime change in Syria he should be ready to invade. Since he lacks the will and the means for this, he is merely heading for a second humiliation. He should back off and deploy diplomacy and humanitarian relief instead. It is not much, but it is better than bombing.