Iran holds elections that, while not perfect, are sufficiently democratic to permit Iranians to make a clear choice of government.
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Saudi Arabia?
Elections?
Not so much.
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The USS Quincy Agreement was one of the fateful mistakes of the 20th Century.
It put America on the wrong side of history in the Arab world.
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The overthrow of the democratically elected Mossadegh government of Iran was another awful mistake, for which John Foster Dulles and Allen Dulles should have been tried as war criminals.  It was a mistake that put America on the wrong side of history in SW Asia.

That mistake has cost over a million Iranian and Iraqi lives, countless billions of dollars, and added to nuclear tensions in a region where there is already an abundance of hatred, suspicion, war and misery. 
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Being on the side of Iran isn't necessarily a good thing, or, as against IS/ISIL/Daesh necessarily a bad thing, either.
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But if you are on the same side as Saudi Arabia, it is always a bad thing.