Reader Mikef at TMV addressed this so well that I will just quote him:
asked the question the other day: for those who believe that we should “go to Tehran”, what gains do you think could be made?
1. We have a mutual interest in a stable Iraq. Iran and it’s neighbors are reasonably concerned that a complete collapse of the Iraqi government would lead to regional war.
2. The Iranians think that they are next on our hit list (which is the obvious conclusion of comments by Bush, Cheney, Rumsfeld, Lieberman etc.) Because of that, its in their national security interest to keep us off balance in Iraq and to undermine us at every turn. Assuring them that we aren’t on the warpath would change that calculus completely.
3. The Iranians share our hatred of al Qaeda and the Taliban. They certainly have intelligence in Afghanistan that we could use. They would support our efforts to quash a resurging Taliban next door.
4. Iran has a strong reformist contingent – members of which would be very friendly to the U.S. and our interests. As long as the conservatives can point to the danger of a war hungry American president, they can rally support from the country (the flip side of our “rally behind the president” fervor after 9/11).
5. Nuclear weapons are expensive to design, expensive to build, dangerous to own and fatal to use. That’s the reason most countries don’t try to make them. Iran is pursuing its nuclear program more in spite of America than for need. If we convinced them that any nuclear attack on Israel would be considered an attack by Iran against the U.S. they’d have serious reasons to invite inspectors in to prove their research was exclusively peaceful. (This was the strategy used by Kennedy to convince the Soviets to pull nukes from Cuba).
6. Despite what some of you seem to think, Iran is not suicidal. They respond to issues of their national security and interest. They aren’t striving to martyr themselves in a suicidal attack on Israel or the U.S. We need to convince them that their security won’t be threatened as long as they behave themselves. Refusing to speak to them sends the opposite message.