The impending U.S. intervention in Syria is a rare case of a major power taking action against its will in order to uphold a greater good: the protection of mankind against weapons of mass destruction.
There is no other ulterior motive. Obama's objective is not to remove Syrian leader Bahar al-Assad or to reverse his gains in the civil war; it is simply to penalise him for violating a universal prohibition and thereby deter further use.
The airstrike reprisals foreshadowed by the United States and France, which are to be strictly limited and proportional to the crime, could thus be called an act of altruism.
The evidence is now compelling that Assad's forces indiscriminately fired chemical weapons on a large scale, killing hundreds of children and other civilians. The leaders of the free world cannot let this deed go unanswered.
Throughout the past year, as the Syrian death count mounted and atrocities multiplied, Obama resisted calls from both sides of the political spectrum for action against Assad.
The small-scale use of chemical weapons in March and April and probably on earlier occasions in 2012 could not be conclusively pinned on the Assad regime.
Having extricated the United States from wars in Iraq and, soon, Afghanistan, Obama was also rightly cautious about not getting stuck in another Middle East conflict with no good options and no clear exit strategy.
The growing role of Al Qaeda-associated fighters in the Syrian civil war increased Obama's reluctance to weigh in in ways that could strengthen these groups.
The need to make clear to Assad and to the world, however, that use of chemical weapons will not again be tolerated trumped other considerations. Other rogue state leaders such as Kim Jong-un are also on notice.
North Korea probably has the world's third largest stockpile of chemical weapons and will be number one in this notorious regard as the U.S. and Russia continue their destruction of Cold War stockpiles. North Korea will have greater reason to think twice about ever attacking anyone with those weapons.
The Syria action also enhances the credibility of the U.S. extended deterrence against nuclear weapons. Chemical weapons have little in common with nuclear weapons except that both have been categorised by the United Nations as weapons of mass destruction.
The term is overused, but it has some relevance in this case. Any nation that uses such weapons or violates treaty obligations against developing them will pay a painful price.
There is also a lesson here for Iran. The punishment meted out to Assad is not intended to give his ally a black eye. But Iran should take notice that the Western powers will take military action when WMD redlines have been crossed. Let us hope that under its new president, Iran will follow through on hints of willingness to curb its nuclear programme.
(Mark Fitzpatrick is director of the Non-Proliferation and Disarmament Programme at the London-based International Institute for Strategic Studies.)