Assaad has created untold amounts of trouble in the region. He supports terrorist activities, he supports Hezbollah financially, with weapons and many other ways. They in turn have ruined Lebanon and are constantly attacking Israel. He controls Lebanon almost as his personal puppet. Working with Iran, he has helped in the killing of our soldiers in Iraq. I personally believe the reports that WMDs were shipped from Iraq to Syria before the war.
Whatever could come to power after toppling Assad can never be any worse than him and could certainly be better.
It could be worse if enough M.Eastern nations come together as one united block...and I do think in time enough of them will unite, be they Shite or Sunni Muslim if they think they can take out Israel...and thereby doing so lessen our presence in the ME.