Many contemporary ethicists, including some Catholic theologians beginning in the 1970's, began to doubt the existence of absolute moral norms. The real world, they argue is free from any moral imperative at all, and within the contingent realm of human ethics, nothing can be for ever.
In Catholic moral theology, even though our human intentions inform in part the moral goodness of our actions, there are nevertheless some actions which in and of themselves are intrinsic moral evils - no circumstances or human intentions can make them morally virtuous or even neutral.
For one important moment, the human community has arrived at a moral consensus approximating a moral absolute: spraying innocent women and children with a powerful insecticide to kill them is wrong. Period. No reasons mitigate its wrongfulness.
Pay attention to those who divert the moral discussion away from the human-pesticide-sprayer and criticize the president who challenges the school yard bully. It's never easy to end bullying and there isn't usually only one answer, but I think we ought be suspicious about those who become furious over the actions taken in response to the use of Sarin, but ignore the crime of using Sarin in the first place.
There has already been outrage, some real and some feigned, over any physical collateral damage from the US air strike, and over any innocent human lives that are lost. The Catholic principles of double effect are helpful in reasoning through those reports.
No more Sarin, ever.