Marc Lynch describes some of the other problems with a plan to arm the Syrian opposition:

First, who exactly would be armed? The perennial, deep problem of the Syrian opposition is that it remains fragmented, disorganized, and highly localized. This has not changed. The “Free Syrian Army” remains something of a fiction, a convenient mailbox for a diverse and unorganized collection of local fighting groups. Those groups have been trying to coordinate more effectively, no doubt, but they remain deeply divided. For all their protestations of solidarity, the Syrian National Council and the FSA show few signs of working well together, while repeated splits and conflicts have emerged in the media within the FSA. So to whom would these weapons be provided, exactly? I expect that what will happen is that foreign powers will rush to arm their own allies and proxies (or are already doing so); which ones are the U.S. meant to choose?

Presumably, the U.S. would end up favoring whichever proxies the Turks and Qataris favor, but it’s a good question that none of the advocates of this option has addressed.

Lynch observes that arming the opposition isn’t going to result in opposition victory:

A second possibility is that they are meant to give the rebels the power to defeat the regime on the battlefield and overthrow it. But that does not seem realistic, since it would require far more firepower than would likely be on offer to reverse the immense imbalance in favor of regime forces. A third possibility is that they are meant to even the balance of power sufficiently to force Asad to the bargaining table once he realizes that he can’t win. But the violence of the escalating civil war will make such talks very difficult politically. The provision of arms is probably not intended to create a protracted, militarized stalemate… but that does seem the most likely outcome. Is that the goal we hope to achieve?

What’s striking about the calls for arming the Syrian opposition is that the proponents of this move don’t even try to sketch out how it would achieve any particular goal. According to Abrams, the U.S. should “defeat” its enemies, as if this is something that is just a matter of will. Drezner suggests that regime change is the goal of his proposal, but he never explains how arming the opposition will lead to that outcome. The answer seems to be that advocates of arming the opposition insist that the U.S. must do something, and this is the one “doable” option that has not already been ruled out. Whether it achieves anything desirable or not seems almost beside the point.

I am broadly in agreement with Lynch on several of his other points. Lynch is right that it is more likely that Assad’s patrons will increase their support in response. I agree that the regime will escalate violence against its opponents. One very good point that I failed to make before is that arming the opposition is most likely a stepping-stone to direct military intervention. As Lynch says, “what is presented as an alternative to military intervention is more likely to pave the way to such intervention once it fails.” We can already imagine how this argument will go: “The U.S. has invested money and credibility in supporting the Syrian opposition, and if we allow them to be defeated it will show the world that the U.S. abandons its friends when they need us most. That will cause our allies to lose confidence in American promises and encourage our enemies, etc.” Arming the opposition is the seemingly less costly way to give the U.S. a new foreign commitment that will become a much more costly one in the long run.