You also ignore the history of Iran and the practices of Shia Islam in particular and make the common mistake of equating Islam as practiced by the people with the Islamic regime. Why would people who oppose the regime dispense with their faith given that until 1979 their faith was compatible with a modern, increasingly secular capitalist economy? Those who are anti-regime are also devout Muslims.
Iran has one of the lowest rates of mosque attendance in the Islamic World. Mosques were packed before the Islamic revolution, but emptied out as people began to sour on the regime, and as religious life became increasingly politicized. Islamic clerics, who were treated with utmost respect before and during the revolution, are now subject to private - and sometimes even open - mockery and hostility.
Really, this speaks more to the failure of the Iranian model than it does to any diminution of Islam in society. What's happening here is that Islam has become tied to an increasingly unpopular, oppressive regime, rather than the leading force in opposition to one, as it was during the Shah's time.