It's definitely a tricky question. On the one hand it sucks to sit back while they're going around chopping off heads, but on the other hand intervention probably won't achieve much. It's like fighting the hydra - you take out one of these groups, it splinters up and reorganises into a new one and comes back and does the same shit.
That said, I support limited intervention from a distance - Destroying their sources of income, decapitation strikes against their leadership using drones, special operations forces, etc. Hell, let PMC's in there to do their thing. I'd be fine with volunteers going over there if they wanted to, we could even have a bounty system or something to make it fun. Give them grief but without going all out and starting another Iraq war.