In addition to being unwise, arming the Syrian opposition likely wouldn’t achieve the desired goal of overthrowing Assad. Spencer Ackerman explains:
Yes, the U.S. can provide lots of hardware, from shoulder-fired anti-aircraft missiles to communications systems to armored vehicles. That military gear can prolong the conflict, preventing dictator Bashar Assad from crushing the rebels. It is unlikely to tip the balance of the war toward the rebels so they can decisively overthrow Assad.
Obama is considering a range of weaponry to the rebels, as described in the Washington Post, including surface-to-air missiles. The idea would be to ship them the weapons, bolster their war effort, and watch them topple the blood-soaked dictator — without a deeper U.S. military commitment.
Except that few strategists consider that realistic. Assad has a variety of advantages — an adaptive military estimated at over 50,000; complete air superiority; chemical weapons — that he will retain even if Obama opens a new arms pipeline. Overcoming those advantages means getting, at the least, U.S. and allied airpower involved — a step the Obama administration, and especially the military, want to avoid. Especially since it might involve shooting down Iranian planes, a fateful step [bold mine-DL].
There’s no surprise that providing arms to the weaker side in the conflict was always going to prolong it. This is what opponents of the idea have been saying for years. Prolonging the conflict until the opposition could prevail has been the goal of interventionist proposals from the start, since their object has always been escalation and eventual regime change rather than mitigating and limiting the effects of the conflict. What advocates for arming the Syrian opposition never explain is how prolonging the conflict would not create even more instability and displace even more people, and they don’t do this because they cannot. Arming the opposition has always been just the first step in dragging the U.S. into the conflict, since it was never very likely to be sufficient on its own to topple the regime. Direct intervention would be the next step that hawks would demand when arming the rebels isn’t “working” quickly enough. In the the event that an air campaign also fails to “work,” there would inevitably be calls for an invasion in order to preserve our “credibility.” If the administration doesn’t want to take these later steps, it should refuse to take the first one.