In the past decade, there have been massive nationwide protests almost annually, often with election fairness as a theme.
The Iranian military has a special wing, the IRGC, that is dedicated to the Supreme leader and used to crush protest or dissent.
These are not characteristics of a functioning liberal democracy. If Iran's regime reflects the popular opinion of Iranians (which I believe it doesn't), then that's in spite of their government, not because of it.