Islam has always had negative views towards Zoroastrianism

This is perhaps too general a statement that leaves no room for understanding the early Islamic period. I just completed the first quarter of an Islamic civ survey required for my MA. This course covered the origins and early Islamic period and I never got the impression that there were inherently negative views of Zoroastrianism within Islam. I have searched through some of the readings required for the course and have posted some excerpts below. I think it is important to remember that Zoroastrians were considered ahl al-Kitab (people of the book) and were granted protection in exchange for the jizyah tax. The Umayyad empire had to deal with the Zoroastrians on a pragmatic level because they were a very large demographic previously under Sassanian control. The initial conquests may have been bloody and violent, but that is not an exceptional sort of occurrence in world-historical terms in which we should single them out as being viewed with hostility. After accepting the new Islamic political order, it seems the Zoroastrians were relatively secure. Richard Bulliet claims (in Conversion to Islam in the Medieval Period) that the pressure to convert was gradual and due to the socioeconomic benefit the Zoroastrians would receive as Muslims.

Whether Zoroastrian communities, found mainly in Iran and southern Iraq, were incorporated at the outset into the growing Believers' movement in some way is less clear. The dualistic theology and fire worship of Zoroastrians must have posed a significant obstacle to their inclusion in the Believers' movement at first. Later Muslim chronicles describe the destruction of Zoroastrian fire temples at the time of the conquest, but it is not clear how reliable such later reports are. Some Zoroastrian communities, like Jewish and Christian ones elsewhere, may have tendered their submission and may have been integrated in some way with the community of Believers. On the other hand, some large provinces of Iran, especially in the north, were hardly penetrated by the Believers for a century or more; the Iranian noble families that traditionally controlled these areas evidently made terms with the Believers early in the conquest era, winning virtually complete autonomy in exchange for remission of tribute or tax payments to the amir al-muminin and his governors. Certainly Zoroastrians continued to exist in large numbers in northern and western Iran and elsewhere for centuries after the rise of Islam, and indeed, much of the canon of Zoroastrian religious texts was elaborated and written down during the Islamic period. Unfortunately, we have far fewer sources for the history of the Zoroastrian communities than we do for the Christians and Jews of geographical Syria and Egypt. We have almost nothing by way of archaeological exploration of predominantly Zoroastrian communities from the conquest era, and the non-Muslim literary sources that inform us about Zoroastrian communities are also much more limited and, in many cases, of later date. - Fred Donner, Muhammad and the Believers

There is an interesting article I have posted below that addresses Islamic encounters with Zoroastrianism. Here is a simple quote that gives you an idea of how the author approaches the subject. Hope you have access to JSTOR.

In short, the victory of the Muslim invaders over Zoroastrian Iran was primarily the triumph of a stronger state, with its superior military power, over a weaker one. Yet, there might also be factors of an ideological nature that might have tended to favor the success of Islam. I would suggest that in at least four ways the teachings of Muhammad would have looked more attractive than those of Zoroaster. First, the former was addressed to all peoples regardless of such factors as race, ethnicity, and language. Zoroastrianism, on the other hand, was a "provincially confined truth." - Marietta Stepaniants, The Encounter of Zoroastrianism with Islam

There's a significant amount of misinformation (or, rather, simply a lack of understanding) of this issue in the thread, and I want to correct some of this.

First, there is a fundamental issue with an assumption you make within your question itself: that the significant influence of Persian culture on classical Islam should somehow be tied to the Zoroastrian religion itself. The main issue here is that, so far as we know, Zoroastrianism had very much been on the decline by the time of the Islamic conquests in the seventh century. While the Shahenshah and a number of important landed elites remained tied to the faith to various degrees, the average number of adherents of the religion had been steadily on the decline for more than a century, and this is born out by the archaeological record, too: plenty of Zoroastrian fire temples had fallen into disrepair well before the Islamic conquests began. Other aspects of Persian culture were far more important and long lasting, and not bound to the Zoroastrian faith at all - Persian attachment and identity with their land, their myths, their language, and traditions more generally (food, clothing, naming practices, etc) made Persia and the Persian people of the seventh, eighth, and ninth centuries CE extremely resilient. The success of the 'Abbasid Revolution and the influx of Persian bureaucrats into state institutions is what led to a greater spread of "Persian" culture with the realm of Islam - Zoroastrianism and its lack of popularity weren't important.

It's strange, because it's a monotheistic religion that influenced Judaism, but Muslims seemed to like Romans much more than Persians.

To call Zoroastrianism a monotheistic religion is to mislead, really, and misses a great amount of the nuance of the classical/late antique form of the religion.

I also don't understand why you suggest that "Muslims seemed to like Romans much more than Persians." Why do you think this?

More generally,the suggestion that the early Arabic sources don't typically treat Zoroastrian's negatively is, overall, fairly true. Islamic law books (dating from the 9th century CE and beyond) often classify the Zoroastrians as "People of the Book" and thus capable of keeping their religion in exchange for the payment of tax (jizya). There are lots of concerns about this, and the traditions which provide justification for this classification of Zoroastrians are extremely dubious, however. Andrew Magnusson has recently completed his PhD at UCSB on these issues very specifically, and if these questions continue to interest you, I would keep a look at for the publication of his dissertation (in whatever form that may be) sometime in the future ("Muslim-Zoroastrian Relations and Religious Violence in Early Islamic Discourse, 600-1100 C.E.").

I hope you have found some of this helpful.

A lot of it had to do with the strength of Persian culture compared to Arab culture. The Persians had an extremely long history of Empire and a general government structure that could be co-opted by the Muslim conquerors. Religion, however, was mostly non-negotiable. Thus the culture survived while the faith withered.

One interesting thing to think about is the fact that Zoroastrianism is easily argued to be a monotheistic faith similar to Judaism or Christianity, but Zurvanism is more inherently dualist. I was never able to find a reliable source on the timing involved in the shift away from Zurvanism, but it may have had some relation to how tolerant the Muslims were. If anyone has any texts that analyze that shift I'd be grateful.

http://www.heritageinstitute.com/zor.../history/postArab.htm http://www.cais-soas.com/CAIS/History/Post-Sasanian/zoroastrians_after_arab_invasion.htm "...most Parsis left their own country, and emigrated to India in the ninth century. Even, at present time, if Iranians are asked about Zoroastrians identity, most of them will answer, those people are fire worshipers and like Jews and other pagans and Christians are unclean people ( See Koran Sura 9 Ayeh 29 ). " http://www.zoroaster.net/indexe.htm