The revolution that took place and put the Islamic Republic Party in place was leftist in style and tactics, and was supported by the Iranian left. They may feel they ended up being betrayed, but any leftist movement or revolution leaves the people who supported it feeling betrayed- it is only a matter of if it happens right away or later.
It was students, as every American recalls, who took the hostages. The left was a major force in the universities of Iran, as is generally the case.
The Islamic Republic Party formed a government based on a form of Islam but with the typical leftist tight control over the economy by the state-- and without economic freedom there can be no real freedom.
The destabilization of the Shah's regime was accomplished with the street demonstrations, propaganda, and general strikes that the left always employs.
It would be incredible naivety for us to believe that the leaders of the SMCCDI have not thought about what their plans are, should they succeed. They have. They don't want to say. They need to if they want to get the support of people like me-- for if they are leftist they will end up under a form of repression just as bad as they live under now, but in getting there there would be many risks for American lives and wasted American dollars.