Iran has been a target of US imperialism for decades, and the US has overthrown their government before and installed a US puppet, just like they'd like to do now. It was even one of the 7 wars in 5 years countried outlined by the Bush administration.
Its not your or my place to choose what form of government they have, that's for the Iranian people to decide. Your place is to oppose the US bombing civilians and sanctioning the country.