And I choose to take people at their word when they say they want to kill me. When the Supreme Leader of Iran says God has brought the Jews to Israel so they can be nuked, I think he is serious. Especially when they are actually building nukes. When their president makes his cabinet swear allegience to the 12th Immam I think he means it. As for a caliphate, again that's their words, not ours. See my tagline.
So some small fanatical groups will try to institute a Sunni caliphate while others try to establish a Shiite caliphate. What do we lose by playing one off against the other? I'd rather they be killing themselves off, then our soldiers.