We kill a couple hundred folks with cruise missiles to avenge a few dozen folks killed with poison gasses and, what? Do the citizens of Syria really need yet another foreign power lobbing explosives into their country? The only argument I hear is that Assad crossed a line and now we have to show him what for. But this sounds like an 18th century aristocrat vowing to defend his honor after an insult. It’s sort of emotionally satisfying — take that, asshole! — but where does it get us except further mired in yet another foreign conflict we have no hope of making better? We look back and criticize the major powers in 1914 for getting involved in the constant squabbles in the Balkans but do the same thing in the Middle East, the 21st century’s Balkans.
Short answer: Because Russia. And were there any other quasi-superpowers [e.g. China] intruding, because them too; we have to protect our interests, and one of these days when there’s nothing else on the schedule, we’ll figure out just what those interests are.
This is not to say that we did a Bad Thing: dropping the occasional MOAB appeals to my sense of noblesse oblige. But if we’re going to pretend that there’s a reason we did it other than because we could — “Well, he needed killing,” said the Texas lawman of legend — the least we can do is go through the motions of announcing a plan, so everyone will have a chance to say “I told you so” when that plan, as it must, goes awry.