"Hardly any Zoroastrian family was able to avoid conversion to Islam when employed by the Abbasids."
I am not taking sides and my Persian history is not as it should be, but I read that there is an ant in Persia that burrows itself into walls under the surface so you cannot see them. One day the excavation is so complete that the walls collapse.
All hadith collections , whether sunni or shia, written by Persians, as well as the historical fairy tales we have in our possession, and you will understand why there is a problem with what SOME Persians did.
Please note the 'some' and do not think every Persian for all time should be blamed.