This is exactly a situation where you have little to no understanding and your naivete is extremely dangerous. If Iran succeeds, it could very well set off not just a nuclear arms race in the Middle East, but actual war on a massive scale. You seem to know very, very little about the Middle East.
Iran is Shia. Shia currently represent about 25% of all Middle East Muslims according to some recent polls. Iran wants to reestablish the Persian Empire. Iran is run by religious fanatics fully capable of making disastrous decisions in the name of their religion, including using nuclear weapons.
The Soviets and the U.S. were much saner and still came close at times to nuclear conflict (Cuban Missile Crisis). Iran isn't burdened with sanity.
Iran has the largest Shia majority, with more than 66 million making up nearly 90% of the population.
Shia are also in the majority in Iraq and Bahrain. There are sizable Shia communities in Kuwait, Yemen, Lebanon, Qatar, Syria, Saudi Arabia and the UAE.
In countries with large Shia communities, Shia often make up the poorest sections of society and see themselves as oppressed and discriminated against.
The Persian Empire spanned from Egypt in the west to Turkey in the north, and through Mesopotamia to the Indus River in the east.
Saudia Arabia has a small Shia population. They are terrified of Iran and have sided with Israel against Iran, even offering to fund the Israeli's air strikes against Iranian nuclear facilities.
If Iran succeeds in getting their nuke and the missiles to deliver them, they have the tools they need to begin to reestablish their empire. Other countries would be forced to go nuclear as well to defend themselves or simply bow down to Iranian aggression. The Saudi's nor the Israeli's will let that happen.
Why would Iran use nuclear weapons? Mahmoud Ahmadinejad and many Iranian leaders believe the most important task of the Iranian Revolution was to prepare the way for the return of the Twelfth Imam, who disappeared in 874, bringing an end to Muhammad's lineage. This imam, the Mahdi or "divinely guided one," Shiites believe, will return in an apocalyptic battle in which the forces of righteousness will defeat the forces of evil and bring about a new era in which Islam ultimately becomes the dominant religion throughout the world.
The Iranians believe it is divinely guided for them to prepare the way for the Twelfth Imam's return.
This represents an existential threat to the world. Imagine the impact a nuclear holocaust would have?
Iran must be stopped and soon. They are testing missiles capable of delivering nuclear warheads. They, even if they live up to their agreement (which they won't) will be nuclear capable in as little as 10 years. Millions upon millions of lives are at stake.
No one wants war. But the much better question is what can be done to save as many lives as possible?
