I'm curious what you know that gives you this impression. Because while Iran reported that the country was >99% Muslim/Islamic they leave out the part where not worshiping Islam is illegal and punishable by death. Independent groups have run open polls and find between 38-50% of the population don't identify with any religion or are atheist, which they'll never admit to the Iranian government. I believe part of the reason they wanted regime change was because they didn't want to live in a theocracy, specifically an Islamic one. So why would they install a new one right after toppling the one they hated? Why would they be burning down mosques now, if they want to return to this again?
@Catch The Rainbow, thoughts on the chances of a secular government in Iran after the current regime is cleared out?
One of the independent groups who I pulled polling data from is
GAMAAN.