Syria is a mess. Assad is killing rebels who - to be fair - are doing their best to kill Assad. And of course the killing is not limited to Syrians who have taken a side. If the US intervenes, it could kill even more people and then support the installation of a government that might be worse than Assad's. If the US does not intervene, it could be standing by while the immoral equivalent of the genocide in Rwanda or the Holocaust takes place. To further compound it, the world community could be facing more situations like this in more countries than it could ever hope to properly address. Anyone who says that it is obvious what should be done .. well, they have more confidence than me.
What is particularly distasteful about this mess from the standpoint of citizens and pundits, though, is that it forces Americans to think. Not just because of the conundrums above but because it defies the traditional divisions. Liberals typically oppose war and conservatives embrace it. In this case, Obama is for intervention and the GOP pundits are against it.
The only good thing about this tragedy is that it seems to be forcing Americans to think for themselves. And for many Americans, that is nearly as uncomfortable as the thought of complete strangers dying.
P.S. For me, the predecessor to a Syrian intervention is a statement of doctrine about when we do and don't get involved in these issues. What conditions would keep us out and which would draw us in? I don't like approaching this as a one-off. During the next couple of decades, I'm convinced that the Internet is going to topple dozens of bad regimes. Any policy we have should anticipate this.