I respect his view here- but he did not say what I believe the key point is... we do not know who the "good" guys are! I've read that the rebels are banning Christians from their controlled territory... if that is the case, I would not support spending a dime or- more importantly- an ounce of blood to put them in power
I've also heard speculation that a rebel victory would lead to pogroms against the Alawite minority. Assad is a rotten character, but it's hardly clear that the rebels would be any good either.