The big difference lies in the difference between Russians and Muslim Persians, at east the their leaderships. Russians are well known for their love for and indulgence of their children and grandchildren. Muslim fundamentalists are known for sending their children out to blow themselves up, if they can just take a few infidels with them. Deterrence may not be applicable to the Angry Ayatollahs and Mad Mullahs. Only if you can convince them that their own person can be endangered do you stand a chance of deterring them, maybe not even then.
You said it, there is no way to 'reason' with madmen.
MAD only works with RATIONAL opponents. The Soviets were by comparison to Islam, incredibly rational.
Even the chinese understand that we can flatten them if they get that stupid. Islam just doesn't care.
They can be deterred. It wasn't a coincidence that they released our Americans the day that Reagan took office.