Apart from, unlike the nerve agent attack here, the alleged Syrian attack could cause a serious escalation of hostilities culminating in global destruction. You have to be pretty damn sure that Russia/Syria did indeed use chemical weapons before military intervention. Like the Salisbury poisoning, none of us here can categorically say who did it or even if it was done. There are enough people saying that what happened is very unclear and on that basis it would be foolish to take any action until proof is evident.