It's quite simple: Al Quada is helping the Syrian people. Supposing Assad eventually falls. How many people will have lost relatives while the west did nothing? How many people will have lost a relative while militant radical muslims were fighting on their behalf.
It doesn't take a rocket scienist to see that if we do nothing (and it might even be too late by now), Syria will be the new recruitment grounds for anti-west terrorists.
America has constantly been at war for a long time, and our economy is paying for it. America can't fight one hopeless war after another. Terrorism IS going to happen. Starting hopeless wars where you cause more damage than the actual terrorists isn't going to solve the problem. Maybe if we were at peace for just a few years, we could fix our own problems.