Seumas Milne writes: There is no limit, it seems, to the blood price Arabs have to pay for their “spring”. After the carnage in Egypt, Yemen, Bahrain and Libya, Syria’s 11-month-old uprising grows ever more gruesome. Four days of bombardment of rebel-controlled districts in the Syrian city of Homs have yielded horrific images and reports from the embattled Bab al-Amr opposition stronghold: of mosques full of corpses, streets strewn with body parts, residential areas reduced to rubble.

Television footage broadcast in the Arab world is still more graphic, and the impact convulsive. Whatever the arguments about the number of dead on either side, the scale of human suffering is unmistakable – and comes after almost a year of continuous bloodletting, torture and sectarian revenge attacks.

So when Russia and China vetoed Saturday’s western-sponsored UN resolution condemning Bashar al-Assad’s regime, requiring his troops to return to barracks and backing an Arab League plan for him to be replaced, US and British leaders and their allies, echoed by the western media, felt able to denounce it as a “disgusting” and “shameful” act of betrayal of Syrians.

But that assumes externally imposed regime change, which is what the resolution entailed, would either work, have legitimacy or actually stop the killing. By decreeing a “political process” with a predetermined outcome, the withdrawal of the Syrian army from the streets with no parallel demand on armed rebel groups, and full implementation within 21 days – with a provision for “further measures” in the event of “non-compliance” – it also paved the way for foreign military intervention.