Those who rightly demand a high standard of evidence for such serious allegations are also obliged to demand that such evidence be urgently collected. But Russia, China, and their many apologists have utterly failed to demonstrate that consistency.
So exactly one year after President Barack Obama declared that he would draw his red line in Syria at the use of chemical weapons, and only two months after concluding that they had indeed been deployed, the message being sent to Bashar al-Assad could not be clearer: do as you please. There is no one to stop you, or even dig up the bodies.
Yesterday, the United Nations Security Council called not for an investigation, but for "clarity", as though rows of dead children with cold limbs and foaming mouths were not clear enough.
This was a veritable diplomatic excretion, not even reaching the pathetic level of a non-binding statement. Chemical weapons are most effective in large quantities against unprotected opponents. Assad previously seemed to be conducting small attacks, under some imagined threshold but also limited in military utility. But those gloves now seem to be off.
The Security Council has been leapfrogged in the past. Both the Kosovo and Iraq wars lacked formal sanction. And yesterday, the French Foreign Minister called for the use of force - provided the massacre was confirmed. His words, though, were doubly shielded: first with his caveat, which he knows cannot be met under the present deadlock, and second with the implicit understanding that it would not be French jets taking the lead in dropping bombs.
He knows this because, contrary to the ravings of conspiracy theorists who interpret every atrocity in Syria as a contrived pretext for a Western war, the Obama Administration could not be more transparent or brutal in its realism. The mass killing of Syrians does not present a threat to the security of the United States, and every military option is deemed to be either too costly, ineffective, or unavoidably escalatory.
In part, this is the same paralysing risk-aversion that one observes in US policy towards Egypt's generals, unwilling to cut aid even when a junta mows down its opponents. Yet more fundamentally, Obama is afraid of winning. As his most senior military officer, General Martin Dempsey, noted: "It is my belief that the side we choose must be ready to promote their interests and ours when the balance shifts in their favour. Today, they are not." This is the misfortune of Syria's chemical victims: to be represented by a plethora of squabbling opposition groups, rebel factions, and jihadists.
Samantha Power, the US ambassador to the UN, wrote the book A Problem From Hell about American inaction in the face of 20th-century genocides. That term ought not to be used lightly, but Syria's horrors echo the paradox she explores: "This country's consistent policy of nonintervention in the face of genocide offers sad testimony not to a broken American political system but to one that is ruthlessly effective. The system, as it stands now, is working."
Today, Samantha Power is an integral part of that system, railing pointlessly against Russian and Chinese obduracy in a New York talking shop. Meanwhile, Syria sinks into its own hell.
Questions after the attack
Could we learn the truth about the alleged gas attacks?
In theory, yes. The nerve agents that Syria's armed forces have - sarin, mustard gas and VX - leave a residue that experts can detect. But the clearest signs fade after about 48 hours, so the tests would have to have been conducted by today if they are to be conclusive. After that, the room for doubt would grow.
Are the experts available to find the truth?
Again, yes. A team of United Nations experts arrived in Damascus on Sunday to find out whether chemical weapons were used during three previous alleged attacks. They are staying at the Four Seasons Hotel in Damascus. Some of Wednesday's attacks took place less than 30 minutes' drive away.
Will they go and find out what happened?
Probably not. The UN team can move only with permission from President Bashar al-Assad's regime. So far, the authorities have not allowed them to visit the sites of the latest attacks. Russia has prevented the Security Council from demanding this access. This is very revealing. If the regime is telling the truth when it denies using poison gas, it would have every reason to allow the UN to see the locations. Instead, Assad is giving the impression he has something to hide.
What about Russia?
The Kremlin's position is also very odd. The Russian Foreign Ministry suggested that the latest attacks might have been faked as "a provocation". So why not allow the UN experts to visit the sites?
What might happen next?
The crisis comes a year after President Barack Obama declared that any use of chemical weapons would cross a "red line". Obama now faces an acute dilemma: act on his warning and intervene, or sit tight and risk losing credibility. If Obama does the latter, Assad would probably conclude that the "red line" is a sham and he can gas his enemies with impunity.
What are Obama's options?
The President has rejected a "no-fly" zone and supplying rebels with advanced weaponry. But Brigadier-General Michael Herzog, a former chief of staff to the Israeli defence minister, suggests a "stand-off air strike against the regime's military capabilities". This would be at long range, placing no Americans at risk, and the target would be an arms dump or an airbase. The goal would be to force Assad to pay a price for his actions. Whether Obama has the required determination seems unlikely.