Who do you think is going to fill the power vaccuum after you bomb Syrian forces into oblivion? The Muppets?
Also, you drastically overestimate the ability of US forces to get all of the weapons. Do you think they haven't already taken measures to hide them? We can't even prove definitively that they used them, let alone figure out where they all are.
When these weapons get into rebel hands, or are about to, what exactly is going to stop Israel from getting involved? And what is Russia going to do when Israeli planes start bombing Russian technicians and advisors?
Seriously, terrible idea. Either you put boots on the ground, preventing Russian involvement, or you do nothing and buddy up to the winner. Which of those options do you prefer?