It seems lot of the discussion on Syria has focused on the share of culpability borne by outside powers. As others have pointed out, there are multiple actors in Syria. Assad/the regime, "moderate" rebels, "jihadist" rebels, ISIS, Iran, Hezbollah, Turkey, the Kurds, the U.S., the Gulf States, Russia, France, the U.K., and other minor players. I hope that was a more or less complete list.
The Syrian Civil War started in 2011 due to popular discontent with the Assad regime. Over a period of several years, it seems to have morphed into an even more elemental ethno-religious conflict based on ancient rivalries, especially Sunni-Shia sectarianism.
To me, this "big picture" perspective suggests that, if not for the Assad regime's unpopularity, as well as these ethnic and religious divisions, there would be no Syrian conflict. That's not quite the same as saying Western powers/Turkey/Gulf states/Russia bear *no* responsibility for the current chaos in Syria. But it suggests these outside players are reacting to events in Syria and attempting to shape them towards their own benefit. Today's French air strikes on ISIS are an illustrative example. Starting conflicts unnecessarily is bad, but I don't think nation-states can be faulted for pursuing their own security interests.