Last March, President Barack Obama explained that the US military had participated in a UN-authorised mission to protect Libyan civilians from the wrath of Libya's regime. He offered a powerful rationale for humanitarian intervention in the face of the brutal onslaught of a dictatorship against its own people. The President said: "We knew that if we waited one more day, Benghazi — a city nearly the size of Charlotte [North Carolina] — could suffer a massacre that would have reverberated across the region and stained the conscience of the world."

When it comes to humanitarian intervention, it appears that size really does matter. Killing a few may not warrant Nato strikes. Killing hundreds — and threatening to massacre the population of a town the size of Charlotte — apparently justifies military intervention. Benghazi was spared the "massacre that would have reverberated across the region" by the intervention of US and other allied forces. With Nato patrolling the Libyan skies since late March, Western consciences managed to avoid the problem that Obama so eloquently invoked — although Libya's civil war has left countless victims. Muammar Gaddafi held on to power much longer than expected; and his opponents are not exactly liberal democrats.

Assuming that the size of the impending catastrophe is a factor in Obama's doctrine of humanitarian intervention, the question must be asked: why Benghazi but not Hama, Homs or Latakia in Syria? Both Hama and Homs are also cities nearly the size of Charlotte, which has just over 700,000 residents. So is Latakia, at 655,000. In all three cities and many other places, a ferocious onslaught continues. A humanitarian catastrophe — nearly 20,000 refugees, to mention one figure among the gruesome details emerging from Syria — has occurred. So where are the cavalry and where is our conscience?

It is entirely possible that the opposition to Syria's President Bashar al-Assad is, like that of its Libyan counterparts, not entirely attuned to Jeffersonian democracy and Western standards of human rights. To be fair, Obama offered other arguments for intervention in Libya, which, by implication, appeared to show where and when it would be ruled out. There is no guarantee that the Libyan rebels will be a better friend of the West than Gaddafi was — the mid — August trip by a Libya Transitional Council delegation to Tehran does not augur well. Neither does the persistent flow of arms from Libya to Gaza, but then Western intervention gives clout to influence the transition. Libya's experience should be proof of the desirability of Western interference with Syria, not the opposite.

There are, understandably, powerful constraints when it comes to Syria. There are Russian and Chinese vetoes to shield Syria; there are limited military resources available; and there are fears of Syria imploding into sectarian violence if the regime collapses, with momentous regional repercussions.