Good essay from someone who actually studies these kinds of things:
The collapse of U.S.-Russian diplomacy and the escalating atrocities in Aleppo have once again opened the floodgates for ideas on how to intervene in Syria. These ideas are all familiar: typically some combination of no-fly zones, air strikes, and arming the opposition. The goals range from civilian protection, to evening the balance of power to facilitate diplomacy, to toppling the Assad regime by force. It may seem odd that these proposals have changed so little over the years despite having failed to persuade previously and despite the dramatic evolution of the Syrian conflict.
This is confusing only if evaluated from the starting point that the purpose of these ideas is primarily to end the Syrian war or to reduce human suffering. For the most part, it is not.
The air of surreality and endless repetition around much of the Syria debate emanates from the mismatch between stated and actual goals. In fact, both advocates and critics of these interventionist ideas generally understand that the limited measures being proposed have virtually no chance of changing the strategic trajectory of the war. The real argument is not over saving lives or even about removing the Assad regime, as laudable as such goals might be. It is over the extent to which the United States should be involved in the war, regardless of whether or how the war ends.
While some surely believe that intervention would reduce the immediate killing or force the Assad regime to engage in more serious negotiations, this is a far cry from ending the war. Limited intervention will run aground of the war’s basic strategic structure...
The cost of this stalemate is an estimated half million dead and over 10 million refugees and displaced. But little has been achieved at this horrifying cost...
This grim logic was obvious quite early on in the war. Once it became clear that early optimism over Assad’s imminent fall had been misplaced and this strategic stalemate set in, diplomacy had to begin from the premise that neither side could win and neither side could lose. Political science studies of civil wars tell us that wars of this type tend to last approximately a decade, and that the number and contradictory preferences of both internal and external actors in Syria make it an extreme version of this type of war. Syria’s war has not been ripe for resolution, either military or diplomatic, and will not be for years to come.
The limited American intervention options on offer over the last few years could never have changed this logic. These proposals, such as no-fly zones or air strikes, would have done little more than move the war more quickly up the escalatory ladder...