I'm assuming Assad gassed those people and I'm assuming that we DO have the evidence. If I am correct on both, then we must give Assad the ass-kicking of the century in order to dissuade him and others from doing this in the future. At this point, we should be working to overthrow Assad and we should form a coalition with our allies to make it happen. He needs to go.
And replaced with what? A repeat of Iraq? A repeat of Libya? A repeat of Egypt? Another vacuum for ISIS to come back and fill? I don't disagree with you on your summation of Assad - he's a murderous thug who ought to face justice for what he has done to his people, but removing him isn't going to improve their situation at this time. Unfortunately, I really think we are looking at a repeat of 1914...tangled alliances, world powers behind proxy militias...US, Turkey, Iran, Russia, Europe, Israel...all in the crucible.