mercilessly prosecuted ...
> Most of the Sasanian Empire was overthrown by the Arabs over the course of 16 years in the 7th century. Although the administration of the state was rapidly Islamicized and subsumed under the Umayyad Caliphate, in the beginning "there was little serious pressure" exerted on newly subjected people to adopt Islam
> Under Abbasid rule, Muslim Iranians (who by then were in the majority) in many instances showed severe disregard for and mistreated local Zoroastrians.
...
Islamic Invasion of Persia was as brutal ...
> However, Sir Thomas Walker Arnold doubts the entire narrative of the forced conversions of the Zoroastrians, citing many examples of tolerance that were shown by the Muslim overlords concluding that "in the face of such facts, it is surely impossible to attribute the decay of Zoroastrianism entirely to violent conversions made by the Muslim conquerors". Arnold suggests that some of the conversions of the former-Zoroastrians were actually sincere citing the similarities between the two religions as a motivation for the conversions. Stepaniants also (like Arnold) declares that some historians have said that some of the conversions to Islam were sincere citing the fact that Islam offered a broader door of brotherhood, unlike the restrictive criteria of Zoroastrianism.
...
Those are choice quotes, sure, but they counter the rather brazen tone of GP's comment. That's even disregarding the fact that the society, norms of war and conquest back then was very different from today.
Umm... don't be my namesake.