The reasons don't really matter. They are all insane to one degree or another. Politics and religion only give some people an excuse, in their own minds, to kill strangers. Or even friends and family. It's only when the insanity becomes institutionalized, as in religion or governments, that the reasons begin to make a difference, and even then only to those who are doing the killing. The dead don't care. The survivors care only for revenge (or justice, if you prefer.)