Why is it justifiable? You’ve failed to make a compelling argument for US aid, much less direct intervention. What strategic interest do we have in toppling Assad? You didn’t even try to make a moral or ethical case for intervention: you just said our “allies” are good guys and you called Assad and his allies an “Axis of Evil", as if name calling was a coherent argument.
Better plan:try diplomacy. Convene a conference with Russia, Turkey, Iraq, Saudi Arabia, Assad, Lebanese Christians, Hezbollah, Kurdish leaders, Iran, Syrian Sunnis, and representatives of other ethnic and religious groups. Then try to redraw the Sykes-picot lines and come up with a new set of nation-states that aligns better with demography and history. If you think that makes no sense, then please sketch out an alternative path to resolving it all. Before we spend another trillion bucks killing another half million people, let’s have some clue about what we are trying to do.