It sounds extreme I know, but here's the thing:
As a theocracy, for the true believers among the population, in opposing the regime, you are literally fighting God's will.
The piety/fidelity of the entirety of the ruling elite matters less than that of the culture that they've installed below them. Because their power is based on the fanaticism of their foot-soldiery, and if say 20% of the population falls into that category...
It occurs to me that for a lot of the IRGC and their supporters a pivot towards moderacy and diplomacy must be unthinkable due to how their more zealous comrades might react.
Mirror fallacy is believing everyone is inherently reasonable and can be reached, a view that is manifestly false. You can see this within our own mostly secular cultures with people who've committed wholly to some faith, cause, or ideology requiring intense deprogramming to bring them out of whatever cult's ensnared them.
Last thing, I personally believe that Islam has many fine qualities. Its principles of service and discipline unto Allah have great merit for instance. But I feel that it unfortunately also -and this is true of all religions to be fair- can be twisted into something truly terrible. Particularly so because of its veneration of sacrifice, with martyrdom being presented as a active practice.
The IRGC sent thousands of children to the front to clear minefields in the Iran-Iraq war... A thing of incomprehensible barbarity to the rational mind, but that's the power of absolute faith for you.