The deal announced yesterday does more than end a specific dispute about Uranium enrichment. That's welcome of course; almost anything that reduces tension between states is welcome.
What it really does is signal the end - well, the beginning of the end - of the mutual hostility between the US and Iran. Much could be said about the causes of this hostility, which goes back at least 70 years, but I want to look forward.
The deal will undermine the hostility of Iran's backwoodsmen to the US. I hope it will reduce the hostility of the US's backwoodsmen to Iran though given Israel's reaction that seems less certain. It will increase the opportunities for trade and other exchanges between Iran and the rest of the world.
It's clear that most Iranians will welcome this. They want better contacts with the rest of the world and many will take the opportunities that will follow.
Will it, as Netinyahu claims, increase Iran's opportunities for military meddling in its neighbours' affairs? Well yes, it probably will. But it will reduce its motivation to do so. Increased meddling might bring back the sanctions that this deal will remove. And as Iran celebrates this diplomatic success it will be more likely to favour diplomacy on other issues.
The Middle East cannot be understood as Goodies versus Baddies. Iran and Saudi Arabia are rivals but both pretty hostile to human rights. In Iraq-Syria we have a least a six-way conflict (Iraqi and Syrian governments, USA, shia militias, secular militias and the Kurds). Iran can be a useful ally in the region (which is not to deny that there will also be conflicts) if we are open to those possibilities.
But the big prize here is increased engagement with Iran. With its unlovely government, certainly, but more with its people. Let's have cultural exchanges and translations to and from Farsi. Let's have international seminars about science, history, arts and politics. Let's have scholarships for Iranians at UK universities and some courses in Persian poetry for UK students.
In short, let's seize the opportunities to learn more about them and to open their eyes to us. Our best argument against fanaticism is our success in creating a prosperous, tolerant and sustainable society.