Time is not on the side of the "humanitarian" would-be bombers.
Here in Washington, at least 162 members of the US. House of Representatives have publicly demanded a Congressional debate and vote before the US takes any military action against Syria. This is, of course, a legal requirement in the United States, under our Constitution and the 1973 War Powers Resolution. The Republicans lost their majority in Congress in 2006 largely because of the Iraq war; so there are political risks here that will be more noticed as the debate widens.
Even before the British vote, the Obama team had less legitimacy and popular support for its proposed bombing than almost any US military action has had in recent history. No UN Security Council resolution, which would be the requirement for legality under international law; no support from the Arab League, nor even one Arab government, which Washington had for the bombing of Libya; not even NATO, which Washington can generally count on for almost any war. And now the UK has refused to join Obama's "coalition of the willing", leaving him with an unprecedented level of international isolation if he chooses to carry out his threat to bomb Syria.
http://www.theguardian.com/commentisfree/2013/aug/30/obama-opposition-mounting-syria-strike