You admit you are supporting people who use poison gas. There is no question about that. AQ and the jihadists are one group in the opposition, and a rather small one.
You demonstrate the weakness of libertarian philosophy: sometimes hard choices need to be made, and liberts cannot make them.
I am not supporting either side of the Syrian conflict. I think they both suck. This is a no win situation for the US. And still no reason has been presented why a military attack is justified. We were not attacked. If we intervene on the side of the opposition, they aren't going to suddenly be our friends.
If they attack our allies - Turkey or Israel, I could see justification for military action. If they want to kill each other off, that is regrettable, but not cause to intervene.