Assad tortured and killed too many children to be supported.
So if you had a junk yard, you would not get a dog that had bit anyone.
Or shoot a gun that had ever killed anyone when confronted with someone who wants to kill YOU.
That is why we will fail.
As they saying goes, there is the world that should be, that you wish it was and the world as it really is.
Following your principles, we never would have joined up with Stalin to fight Hitler and you would be a German citizen today, unless you are a Jew in which case you would not even exist.
We are not in a position to be picky about our choices.
This is going to last a long time. We either support someone who is already there and knows all of the inside workings, or we have to put 500,000 troops over there for 50 years.
The idea that we have approached the age of clean wars where one can sit at his computer and beat the enemy into submission without hurting anyone except the bad guys is a false idea.