How is it that the method of killing merits a greater response than the quantity of those killed? North Korea, for instance, kills tens of thousands of innocents per year and imprisions hundreds of thousands (most of whom die a slow and painful death of starvation and disease). I guess Kim is safe so long as he doesn't gas a few hundred?
Kim is safe as long as he has the means to level Seoul, for one. If we believed that Assad would completely destroy, let's say Rome, we'd leave him the fuck alone.