I have expressed support for the U.S. decision to try to undo one of the negative effects -the creation of the Islamic State- of some of its previous mistakes -most importantly the second Iraq war- by bombing Islamic State positions, and a few times also al Qaeda positions. This bombing campain has been crucial in preventing the Islamic State from taking the Kurdish city of Kobane and arguably also Baghdad and Iraqi Kurdish areas.
However, another part of the U.S. strategy against the Islamic State, arming so-called “moderate” rebels in Syria is mistaken. The so-called “moderate” rebels (who often aren’t so moderate as Obama claims and are often allied with al-Qaeda) generally only fights the Islamic State because the Islamic State attacks them. They almost never launch an offensive against the Islamic State and instead views the Assad government as their main enemy.
And while I certainly don’t deny that the Assad government is vile, it is nonetheless far less evil than the Islamic State (and al-Qaeda and most other non-Kurdish Syrian rebels) and it is the military force that has the greatest capability of repelling the Islamic State.
By arming and supporting allegedly “moderate” Syrian rebel groups, you will force Assad to distract more of his military forces to fighting them, strengthening the Islamic State.