I don't think morals should always guide foreign policy. So although I think it is a moral imperative, the question if and what should be done is a different question, as far as I am concerned.
But if you ask me for moral obligation, I'd say yes, because ISIS is a result of the vacuum that came out of the flawed US Iraq invasion and very inept post-war reconstruction. I was against the Iraq war, among other reasons exactly because I was afraid something like ISIS might happen, but since the war was done, it is now America's responsibility to restore order post-war. The reconstruction and stabilization was obviously not finished yet.