See
Not a word on assad helping purposely birth ISIS, on his regimes actions pushing people towards ISIS, on his current plans (with russia and iran) undermining the effective fighters against ISIS - all part of wider moves to wipe out moderates, democrats, left-wing or secular rebels with the help of Iran, russia and hezbollah in order to leave it a battle between his dictatorship and ISIS. Exactly the same logic as ISIS' removing the grayzone. The grayzone being of course those sensible non-islamist and non-mass murder non-assad supporters.