Although I agree that the actions of IS are despicable and cannot be morally justified under any circumstances, the idea that western air strikes on them is going to be of any benefit to western countries whatsoever is utterly absurd. Every time a western country intervenes in other countries (particularly Muslim ones) they end up killing scores of innocent civilians and alienate a large proportion of the population against them.
Bombing the Iraqi army positions (when Saddam was in power) and bombing the military hardware of the ISIS is entirely different. When NATO invaded Iraq, there were no justifiable reasons. All the BS about WMDs and chemical weapons were just made up in order to justify the invasion. But ISIS is posing a great deal of threat to very survival of the Iraqis, especially the minorities.
Also, the NATO has moral responsibility to deal with the ISIS, as the latter had emerged through the vacuum they left after toppling Saddam.
It is not different, where do you think IS comes from, they were funded and equipped by western countries for fighting against Assad in Syria. So they are allies whilst in Syria but when they cross the border into Iraq they become enemies. If we didn't want IS, then we shouldn't have funded them in the first place and we certainly shouldn't continue to fund them now. Western countries have done this for decades, funded terrorist groups when it suits them and are then surprised when the terrorists don't care about western countries.
Additionally, the idea that the US actually cares about Iraqi civilians is laughable, they launched an illegal war against them on a pack of lies whereby hundreds of thousands of Iraqis paid with their lives. The US knew this at the time but proceeded anyway so that they could secure Iraq's oil and steal billions of dollars of Iraq's wealth. They had no regard for them then and to assume that they do now is incredibly naiive.
As for the point that NATO has a responsibility to intervene, this is the kind of mentality that causes us these problems in the first place. NATO was set up to be a defensive organisation to defend the territory of member states, not to go around the world acting as the worlds policeman. NATO has become an extension of western foreign policy to enhance US imperialism and implement its will around the world. If anyone should intervene against IS, it should be the Iraqi people themselves or neighbouring countries that face a direct threat from IS, there is more than enough military capability in the middle east to tackle IS. The arrogance of the west that they know better than everyone else has caused us many problems for decades and will continue to be the case into the future unless we seriously change our approach to foreign policy.