I will admit that this is hardly optimal:
The Obama administration secretly gave its blessing to arms shipments to Libyan rebels from Qatar last year, but American officials later grew alarmed as evidence grew that Qatar was turning some of the weapons over to Islamic militants, according to United States officials and foreign diplomats.
Jihadis in Syria seem to be getting arms disproportionately, too.
But we had to make the same bargain with the devil in World War II. Obviously, we armed the Soviet Union to keep them in the fight. Less known is that the resistance movements we armed in Nazi-occupied Europe had communists as the ones who fought the hardest. The Partisans were armed by us to defeat the main enemy. And after the war, Euro-communists (on the surface independent but secretly pro-Moscow) were a problem for us in France and Italy, especially. They took power in Yugoslavia, of course, although those communists did reject Soviet dominance.
And let's not forget who we had to arm to defeat the Soviets in Afghanistan.
Stuff happens.
More important than the fact that weapons leaked to jihadis is what we tried to do about it once we figured out what was happening.
Of course, we could go back in a pointless debate over whether we should have intervened in Libya over humanitarian reasons when Europe was capable of handling Khadaffi without us (even if not nearly as effectively without our capabilities). I thought we had other things to do. Like getting a status of forces agreement with Iraq. But I digress.
In practice, the Obama administration seems to have rethought the idea of direct intervention under Responsibility to Protect given we've largely watched Assad slaughter his people for the last couple years.
The sad fact is that it isn't usually possible to arm the League of Women Voters to fight against tyrants. The world is an ugly place and sometimes you have to deal with ugly actors who temporarily share an interest.