As an Israeli citizen (and an aging reservist). I mean, what happens if Hezbollah starts raining missiles at the population like in 2006. Would the US strike them too, on Lebanon ?
Would the IDF respond, and we have a repeat of the 2006 war ? Would a hastily assembled US coalition fall apart if IDF jets strike against Lebanese targets ? It is not going to be as easy as Israel sitting out the Gulf wars.
I think taking so much heat, for Israel (and maybe the US too), would be worth it if we were talking about the Iranian nuclear installations.
Everyone is talking as if not bombing Syria would be a green light for Iran, as if it means the US has no credibility. But this would only mean anything if you believe the Iranians are serious about the talks, and might budge if they thought Obama might actually drop the hammer on them. However, if you are of the opinion that they are talking just to stall, then it doesn't really matter how they perceive the US projection of power. Furthermore, any complication of a strike in Syria, would make a strike against Iran (the true target) less likely.
And all that, doesn't even start considering things like the US public image, the economy, ethics.
Assad using sarin gas is terrible, but I really don't believe anything good can come out of foreign intervention. It's not as if the rebels are any better. The Arab guys at my workplace say there are videos of Chechnyan fighters doing all sorts of nasty stuff, like eating a human heart.