Look if people want to believe that a regime change in the Middle East that has been LESS thought out than the grand adventures of GWB is likely to ultimately turn out well then I don't know what the fuck to tell you.
Iran's population 90 million. Iraq 45 million (was 27 million in 2003). And while Iran has multiple minority groups (Kurds, Baluchis, even Arabs, I guess count as such), it doesn't seem to have a situation akin to the Sunni-minority-rule situation that characterised Iraq. So, yeah, doesn't seem likely to go better than Iraq did.