At this point let Iran build their damn nuke. [View all]
Let them build a delivery system for it. Hell, let them have a half dozen, or a dozen. It really doesn't matter.
Nukes are, in many ways, the most useless weapons in the world. Countries that have nukes aren't going to be the first to drop them because they know if they drop them their nuke equipped opponent, and/or allies will retaliate with nukes in an act of mutually assured destruction. That's the reason why, over the decades since Hiroshima and Nagasaki, through the ensuing chaos and military posturing of those years, nobody has dropped the big one. He dies, she dies, we all die, and not even the craziest leaders in the world want that(looking at you here North Korea).
The only thing a nuke is good for in these times is security, the security blanket knowledge that a country can retaliate if push ever comes to shove.
So let Iran have their security blanket, it will actually a take bone of contention off the table, calm matters down, and real progress can be made on the diplomatic front instead of fighting about a weapons system that will never be used in an offensive capacity. Otherwise we're just going continue to see more ongoing madness, taking lives, destroying countries, all over the most useless weapon in the world.