One of the biggest reasons why it wouldn't be necessarily bad if Iran got nuclear weapons. Iran is fairly ethnically diverse, but their constitution is fairly clear about equality between those groups. The CIA has actually tried to destabilize Iran by inciting ethnic tension, and it didn't work. Iran is a strong, democratic and stable country with a loudmouth president who knows better than to match his words with actions, there's not much to be worried about giving them nuclear weapons.
Israel being the sole nuclear power in the region is pretty dangerous. The one deterrent they have against using them is losing the support of the United States. If Iran got nukes it would force peace talks on Israel across the board, a lot of concessions by both sides and a huge decrease in violence matched with an increase in diplomacy. The region is a mess, and giving the most established powers on both sides nukes will put everyone on their toes.
Most of you are so programmed with the "axis of evil" drilled through your thick skulls that you can under no circumstances view the international system from the lens other than that of an American. It's really a waste of my time to even argue this point.