Iran is a democracy!
And if Iran wanted to build nukes nobody could have prevent it from happening. Just like they could never prevent Iran from acquiring nuclear energy and enrichment science, air-defense, beyond advanced radars, ballistic missiles, submarines, nano technology, cloning, stem cell research, cancer treatment, Space program, and a million other advanced sciences they tried to prevent Iran from acquiring (by murdering the scientists as I explained in OP) and failed...
The US regime simply does not have the power to prevent any of it.

The only reason why Iran has not moved in that direction is because of Islam.

According to the fatwa of Ayatollah Khamenei (Imam of Muslims), nuclear weapon which is considered a weapon of mass destruction is haram.
Same situation existed back in the 1980's during Imam Khomeini time about chemical weapons during the time when the same Axis invaded Iran and was using chemical weapons against Iranians (bombing cities with it). When military commanders went to him as the "commander in chief" to get permission to acquire chemical weapons to respond to the enemy in the same manner, he did not allow it. WMDs are considered haram.