Firstly let's do away with the simplistic initial forced conversion by the sword, which is a myth. Mass conversion within a short period of time didn't happen either, it was a gradual process. The Arab rulers didn't really want mass conversion initially because Muslims had preferential tax rates, so ruling over none Muslims made more sense economically. Because of the preferential tax rates for Muslims and the social mobility more and more people converted. Initially Zoroastrians were considered 'people of the book', which was a higher social status within the state but later under Abbasids rule they were downgraded to 'unbelievers' and discrimination towards then and their civil rights were vastly eroded. Their temples were often destroyed and their possessions confiscated. The persecution worsened and eventually many Zoroastrians fled Iran to India, essentially refugees. Many that stayed under Safavid rule subsequent were forced to convert or die under the sword. Throughout later governments Zoroastrians became further persecuted and their civil rights completely eroded by religious persucution.