US-Iran relations are durably crippled by the fact that we don't trust one anothers intentions. Iran has a very different conception of what NATO is trying to do in Afghanistan than we do, and this likely puts a low limit on how much they would support our mission. At the same time of course, Iran doesn't like the Taliban either; afterall, they nearly went to war with it in the 90s. Iran, just as it was 1000s of years ago when it conquered its first empire, is still somewhat infatuated with the ideal of the enlightened theocratic despot. Now they call him the Supreme Ayatollah. The west may dislike this ideal, but it is something qualitatively different than a bunch of brutal fundamentalist desert tribesmen romping around and killing people and blowing up priceless statues. AKA, those are two different forms of religious radicalism whose differences make people who hate us also hate eachother. To be fair, however we may differ in principles, Iran's government does seem to be basically humanitarian. Iran's government isn't so bad, but it will never trust us without us doing things we won't do, like abandon Israel, so I see potential for cooperation as limited. Nevertheless, we should be open to it when the possibility presents itself to us.