Jim Geraghty over at National Review Online attempts to answer a question I've asked here - why is it so terrible that 1,000 people were killed with sarin gas, but the 110,000 (so far) killed with bombs and bullets, not so much.
He points out that "Leaders from Moscow to Beijing to Washington to Havana concluded that chemical weapons are fundamentally different from the ‘standard’ and necessary tools of war." and thus we have a uniformity of moral opinion on the question.
We must first note that many of those leaders and the countries they represent are known for considering treaties as primarily useful for restricting those more honorable than themselves, but not particularly binding on their own actions.
I must also demur from Geraghty's implication that signing this treaty, and even abiding by it, constitutes the rendering of such a moral judgment. It does not. As Geraghty notes in his own post, chemical weapons are terribly inefficient. They require a more-or-less fixed target which can be difficult to come by when dealing with a highly mobile modern enemy. They require ideal weather conditions or they become as much a threat to one's own forces as the enemy's. They can be difficult to safely transport and reliably deliver on target, too.
I really don't know what the Assad regime was trying to do with the use of those weapons in this case, but if their object was to persuade their enemy to lay down his arms, they failed. If their object was to reduce their enemy's ability to wage war, they failed. The Hussein regime in Iraq managed to use chemical weapons against Iran in a militarily useful manner, but on the whole chemical weapons don't do a whole lot to help you war.
That - not some faux moral unanimity - is why 98% of countries signed on to the ban.
Killing these civilians by chemical weapons is not morally different from killing them by other means. It was immoral, but would have been immoral regardless, although we must remember that the distinction between combatants and non-combatants is a Western, indeed, a Christian distinction muslims have never accepted.