If ISIS restricted their killings to Christians and other non-Muslim groups, Obama would not be concerned. But they kill Muslims so he finally concludes that they are bad.
Slaughtering innocents is how the Muslim caliphate went from controlling part of Arabia on Muhammad's death to ruling from southern France to the Indus Valley just 100 years later.
In I Samuel 15.3, Saul is ordered to kill all the Amalekites, "man and woman, infant and suckling." His failure to do so leads to his being rejected by God. Not that Obama would be familiar with anything in the Bible.
Actually a number of liberal churches condone abortion, which is the killing of innocents.