To be fair, it would also be pathetic through and through (it really, really would) to claim that this deed has nothing at all to do with religion (in this case, radical islam), if one is deluded/desperate enough to even try such an angle after his pledged allegiance became known, or that ISIS (and comparable islamic fundamentalist terror groups, such as Boko Haram and al-Qaida) isn't a major source of inspiration for people that's both considering deeds like this and has some sort of pre-established connection/logical route towards, on some level, embracing such tenets. I mean it's certainly perfectly fine to talk about american societal issues (such as gun culture) or what have you, and discuss what part those plays in encouraging/making a thing like this happen, but limiting the discussion to that, particularly so in this very case, is even more asinine than straight out fully blaming moderate islam as a concept (and that's a feat, really).