Let me state what the potential problem is: a nuclear-armed Iran. That would put the bomb in the hands of a radical theocracy, swimming on a sea of high priced oil, whose president has denied the holocaust, threatened to wipe Israel off the map and to attack us. 
 
In my view, Iran probably would not use a weapon against us or Israel or give the technology to terrorists. But it would feel emboldened to make even more mischief in the region. And if Iran gets the bomb, that could well fuel an arms race with Sunni Arab countries like Egypt and Saudi Arabia, making an already volatile region even more dangerous.