Moral Consistency & Military Action in Syria

An act of war against a nation that is not threatening us has unpredictable consequences, almost all on the downside.

Supporters of US military action in Syria (and elsewhere) must therefore have certainty that the good done and the lives saved by the action exceed any harm done, most of which is unpredictable and all of which is uncontrollable. They must also be sure that the information that they use to justify the action is beyond reasonable doubt.

Put another way, the certainty of the harm done must be matched by moral and informational certainty of those doing it. Is it as we intervene in Syria?

Also, if the case is that clear, why violate the Constitution by not requesting the support of the people, in whose name the violence is being done?