It lets them live, and not too restrictive if they're not too provocative.
It also kicks the can down the road 15 years. Zionistan will still be there; they've got a lot of nukes, and they've developed a right wing empire mentality.
This is really between the Shia and Sunni and has been going on for centuries. I read Shia translates to something like "partisans of Ali (Mohammed's son?) and the Sunni followed a different branch. To paraphrase William of Occam, you should not multiply bullshit unnecessarily. This isn't going to end anything; you don't need nukes to wreak havoc, the underwear bomber fucked up US travel with virtually nothing. Anybody with high school chemistry can blow shit up; morons can put a magazine in a AK47. The tribalism is more dangerous than the technology.