Guess it all has to do with the role you envision for the US.
I believe, if we are going to play the good guy and the planet's
police force, we should act to protect the citizens of Syria. The
fact that Assad is a tyrant adds to the impetus to act.
Do we worry about public opinion, Yes, it is obvious. Hell the
Isolationists and Charles Lindburgh kept us out of WW2 until we were
attacked by Japan and war was declared on us by schikelgruber.
If the past hasn't been able to teach us the lessons we should have
learned : Cleaning up N Korea and China in 1948 for instance. The
future will not allow us the benefit of a lot of time to react.
Initiative has always been a desired condition.
I don't know the best course for our involvement in the ME, but
if we are going to maintain a presence there we might as well
not play footsie with Iran and her allies, Syria for one.
The longer we wait the worse it will be.
Deja vu, We could have helped the Hungarians in their rebellion
against the USSR. We didn't, And it took another 40 years to clear up.