It is optimistic, but not naive. I'm not saying that our relations will in any way reduce the two sides' hatred for each other. The US now has a vested interes

It is optimistic, but not naive. I'm not saying that our relations will in any way reduce the two sides' hatred for each other. The US now has a vested interest in reducing tensions between Sunnis and Shiites. If we have a diplomatic partner on one side of the fight (e.g. only the Saudis), our response must be to either support their interests in the region or stay out of it. If we have interests on both sides, our options are to either push for peace or to play the sides against each other in hopes of chaos and a mutual weakness. We may end up pushing for the latter, as was the case in the Iran-Iraq war, but with a shared enemy in the Islamic State and our long-overdue recognition that chaos hurts our own security and economic interests, it is in our own self-interest that we advocate for stability. Let me be clear: both Iran and Saudi Arabia are ruled by theocratic despots. They will continue to revile each other and assert themselves in the region. But it is far easier to turn a blind eye on their bad behaviour when we have no other option (both in SA and Pakistan.)