"destroy democracy in Iran"
Why do people keep on saying this when it's an utter falsehood? You cannot destroy democracy where it never existed.
Could you elaborate on that? Mossadegh was nominated as Prime Minister by the Majlis, so unless you think that the Majlis wasn't elected in a proper manner he was democratically elected (women didn't have the vote but since you are not exactly the "I am a male feminist" type that is likely not what you are talking about.
).
The exceptions to full adult suffrage don't seem so bad for the time and context: women, foreigners, under 25s, "persons notorious for mischievous opinions", convicts and ex convicts, active military personnel.
Iran was a constitutional monarchy with a Parliament and such systems do have a democratic element, which the Shah (with US assistance) blocked from increasing its power, thus curtailing a process that was heading towards parliamentarism and full democracy (or that is at least a reasonable interpretation - we will never know for sure). What happened changed a constitutional monarchy into a de facto absolute monarchy.
Iran was constitutionally where a lot of European states were in the second half of the 19th century that are generlly considered developing democratic in that era. The Shah had a habit of firing his PMs at a rapid pace, but if Mossadegh had been able to stay it looks likely they could have continued down the same gradualist path to full democracy that constitutional monarchies took in Europe. At least the US backed "operation" blocked any possibility of that happening.
