I've been curious myself about why the activist class seems weirdly quiet on this issue.
On a quick scan of media feeds I've seen a couple of things that stand out (I do not confirm or deny how true these claims are)
1) Current Iran is a enemy of the USA and thus activists can't support the destruction of the current regime. Iran is able to create nukes so can put pressure on the USA in Middle East Politics (esp. Palestine and Israel)
2) The uprising and the Shah are CIA/Western Backed and thus supporting the protestors is de-facto colonialism/imperialism.
3) Contrary to popular belief Iran is not actually a Muslim nation, only the leadership is. The population is significantly more varied and people do not want to be seen supporting the firebombing of Mosques because Islamphobia.
I don't know how widespread these opinions are, but it IS very strange how I don't see more outrage.