Jimmy Carter refused to back the Shah a shining light at the time who attempted to reform the Ayatollahs.
The Shah and his secret police were about as much of a shining light as Saddam Hussein in Iraq. Jimmy Carter couldn't cure the Shah's cancer or megalomania. And so far as reforming the ayatollahs, the Shah inflamed things by having his minions criticize Khomeini as a drug addict, homosexual, British spy, etc.
Again, is Iran's gov't any worse than the Saudis?
It used to be that Iran was meddling in other countries, especially Lebanon, while the Saudi were more insular. But the Saudis decided to go global and export their extremist and intolerant version of Islam. And then go militaristic bullying invading and destroying Yemen, blockading Qatar partly because they have actual free press, kidnapping the head of Lebanon and forcing him to resign. They also have a lot of heads of state on their payroll, including in Lebanon, Sudan, CAR.
Of course since the Saudis are allies, we allow them to rampage around and foment wars and destabilize other countries while demonizing Iran for acting similar. Of course the US destabilized Iraq (an understatement) so that now the Shiites run the show there, giving Iran another significant sphere of influence. The US often shoots itself in the foot in the ME. If the US-backed Shah hadn't been a murderous repressive megalomaniac dictator, the country could have transitioned to something more modern and pluralistic. Of course Iran tried to do that back in 1954 and we had their head of state assassinated ...