In fact, we believe - quite rightly - that if the US had conditioned military assistance to Israel on appropriate care for civilians, then the awful tragedy that unfolded in Gaza could have been averted. Similar levers for changing the behaviour of Iran do not exist.
What about the 1953 CIA/MI6 coup that overthrew Iran's elected prime minister?
And there have absolutely been examples of mass protest movements against regimes that are hostile to the US that are committing crimes against humanity. Years ago I went to a huge demonstration about the genocide in Darfur on the national mall in Washington. Raising awareness of what is happening and putting pressure on the Iranian regime (and on Western governments) can have an impact regardless of whether or not the West is hostile to Iran.
What you saw in Gaza was ALREADY incredible levels of care and restraint (that has cost many Israeli soldiers their lives) to minimize civilian harm, when fighting against an enemy that benefits from increasing said harm.