The U.S. and "the West" in general suffer from what might be called democratic chauvinism. These countries presume that liberal or constitutional democratic republics are really the only legitimate form of government on earth, and reserve for themselves the right to determine whether any government that isn't such a republic is a threat not just to world peace or order, but to "freedom" as well. Some regimes, like the monarchy of Saudi Arabia, pass the test because they have something to offer and are willing to deal with us. When that isn't the case, the West has few reservations about demanding "regime change" as a moral imperative. To the rest of the world this looks like western imperialism or "arrogance," but the example of Turkey suggests that such arrogance may come inevitably to republics, wherever they emerge. Turkey has been a republic for nearly a century now, not counting periods of military rule. The republic's Islamist leader is accused, inevitably, of "authoritarian" tendencies both by outside observers and domestic opponents, but President Ergodan shows what might be described as small-r republican arrogance when it comes to his neighbor, Syria. Turkey showed some reluctance about joining the coalition against the self-styled Islamic State a little while ago, but with the IS driving Syrian Kurds across the Turkish border into refugee camps Erdogan now vows to fight the IS. But just like the Americans, he stubbornly refuses to recognize the most obvious, if not most necessary ally against the takfiri headcutters: the Syrian government. In practically the same breath, Erdogan says "we will continue to prioritize our aim to remove the Syrian regime." No doubt, also like the Americans, he assumes he can find rebels capable of toppling Bashar al-Assad, yet incapable of becoming a threat to his own country's interests.
In Turkey's case, this may be less democratic chauvinism than plain old Sunni chauvinism. The Turks may hate Assad less because he's a tyrant than because he's an Alawite -- though for all I know they may think him a tyrant because he's an Alawite. Like other Sunnis, Erdogan probably considers Assad too friendly with Shiite Iran. But worrying about Iran -- as the government of Israel also recommends to everyone -- seems to be a priority error at the present time. The IS, after all, is the latest existential threat to global peace, order, freedom, etc. Their high-profile but limited-scale atrocities have stigmatized them as the barbarians of the hour. Some people, no doubt, regard the self-styled IS caliph -- a figure who seems to keep a relatively low profile, at least as far as western media is concerned -- as the next Hitler. But if "next Hitler" is anything more than a rhetorical device, might the world not learn from how it dealt with the first Hitler? Wasn't it Winston Churchill, idol of neocons, who said, to justify Great Britain's alliance with Stalin's USSR, that if Hitler invaded Hell he'd make an ally of the Devil? It's all about priorities. The "greatest generation" understood this, so it makes sense that an American veteran of World War II, George H. W. Bush, having identified Saddam Hussein, however foolishly, as a "next Hitler" after Iraq invaded Kuwait, went to the trouble of assembling as broad a coalition as possible against Saddam -- including Syria under Bashar al-Assad's dad. It should be a matter of common sense, should you find a threat to global peace striving to overthrow a country, to join forces with that country's government, whether you like it very much or not. But that pragmatic step is morally or strategically unacceptable to Americans and Turks alike. It's reasonable to assume that each group is more interested in having their man or clique in control of Syria than in eliminating the IS. Each probably wants to blame Assad for the rise of the IS -- for not disappearing conveniently when asked, or for not getting killed in a timely manner -- but the impulse from outside to destabilize Syria probably keeps the IS going more than anything else, even if no outsider really wants them to take over. Like it or not, the surest way to suppress the IS in Syria is to shore up the Assad regime. That doesn't mean Assad is a good man or a good leader or that Syria needs a dictatorship or whatever else you might infer. It means that the world -- the Americans, the West, the Sunnis -- needs to stop fantasizing about third forces and make the only choice possible in Syria, apart from letting history run its course.