The essential problem is that in there are currently two likely choices in the Middle East; vicious dictators who protect minorities and Islamic fundamentalists who oppress everyone and kill off minorities. Egypt may turn out to be a third option, a benevolent plutocracy, but they will get there on their own without need for American military intervention.
If we support Assad we can help ensure there will be no genocide directed against Christians but then we're effectively supporting his mass murder of dissenting civilians who just want to be free.
If we support the rebels we can help end Assad's oppression but from what we can see the Islamic nuts will be able to wage war against Christians.
If Obama had acted 2 years ago, instead of praising Assad, when the rebels were mostly good Muslims who had no problem with a multi-religious society things would have been different.
But now there is no good reason for us to intervene in Syria to help decide who wins.
The only rationale for any sort of limited strike is to teach governments that they can't use nerve gas on their people but the reality is that Assad has killed a lot more innocent civilians with conventional weapons than with nerve gas so any strike would be unlikely to stop the real problems of governments killing their own people.
I don't believe we ever need to get the worlds approval to employ military force when we're in the right, say liberating Greneda, no amount of world approval can make a military intervention that does not accomplish anything beneficial for either the USA or the people of the country we intervene in a good thing.
But if we don't follow through on Obama's commitment then our enemies will doubt our will; Clinton's running out on Somalia convinced Ossama that he could attack the US with impunity.
The good news is that no one is afraid of Obama nor does anyone think he'll do anything militarily in response to foreign aggression so the US can do the right thing, not attack Syria, comforted by the knowledge that Obama has already ensured that the enemies we should be scaring already know that Obama's America will always look for compromise.
In the playground that is the world the bullies already know Obama will give up his lunch money without a fight.