A logically prior question is: does the US have the right to attack Syria?
In fact, it does not. Consider Article 2 of the Charter of the UN. All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state. Notice that this bans the use of force and also bans the threat of force. So Obama is violating the UN Charter even by threatening to attack Syria. Since the US has signed the UN documents, this provision of the UN Charter is binding on the US government.
Syria has never attacked the US. If the US does attack Syria, that will constitute a war crime. Launching a war of aggression was termed "the supreme war crime, a crime against peace." Top German leaders were hanged at Nuremberg for this war crime. Justice Robert Jackson, chief prosecutor at Nuremberg, declared that “To initiate a war of aggression, therefore, is not only an international crime; it is the supreme international crime differing only from other war crimes in that it contains within itself the accumulated evil of the whole.” Mike Ratner, head of the Center for Constitutional Rights, makes the point that a US attack on Syria Violates International Law.
In his speech this evening, Obama went on and on about how terrible chemical weapons are. He claimed that the US was working to ban chemical weapons. However, he omitted four very relevant points.
(1) The US used chemical weapons - Agent Orange and napalm - against the civilian population of Vietnam, Laos, and Cambodia. We killed three million people in order to demonstrate to the world American "leadership".
(2) In 2004, the US attacked the Iraqi city of Fallujah using white phosphor and depleted uranium, which of course are chemical weapons.
(3) It is a fact that Israel used chemical weapons against Gaza in recent years, burning civilians with white phosphorous. That was a war crime and a crime against humanity, in the words of the Goldstone report, commissioned by the UN. Nobody held Israel accountable, nobody talked about bombing Israel. Instead the US government voiced full support for Israel's use of chemical weapons. There is no way Israel would have attacked Gaza refugees without US support.
(4) Finally, while Obama was eloquent about how terrible it is to kill women and children, he forgot to mention that he has killed about 3,000-4,000 people in Pakistan and Afghanistan using drones, and an estimated 74% were civilians who happen to be in the wrong place. Here is a story from the Washington Post two days ago. Here's a story from last year by Gareth Porter, the source of the 74% figure, Cover-Up of Civilian Drone Deaths Revealed by New Evidence.
Funny how Obama omitted these four devastating points. Most of the pundits and politicians never mention these inconvenient facts. These facts have disappeared down an Orwellian Memory Hole. But while few are voicing these sentiments inside the Washington beltway, many are voicing them around the world.