An extremely good question!!!
Why not check out WHAT Zarathustra's so called religion consists of?
Have you never heard that the one thing Tolerance is intolerant of is Intolerance?
Tolerance has to be intolerat towards Intolerance to stay Tolerance, otherwise Tolerance would not have any meaning as Tolerance whatsoever.
I would say exactly the same thing goes for Zarathushtra.
His "religion" is not his property, the way Islam is Muhammed's property (Allah is God and Muhammed is his prophet etc) and the way Christianity is the property of Christ (after all, Christ and nobody else is the Son Of God, God incarnated). THERE we can speak of two intolerant religions. Obey, or go to hell!
But what is Zarathushtra saying?
He is saying that MAZDA (intellect) is the ONLY thing worth worshipping/celebrating for us as human beings. But what is Mazda then?
Zarathushtra frankly does not care whether we regard this message as his "property" or not. He is totally open to the possibility that we can reach this conclusion without him. This is the exact opposite of Islam and Christianity with their "copyright founders".
Because against Truth stands Falsity and Truth is never Truth unless it is intolerant towards Falsity.
That's just the way it is, whether you like it or not. This is why Mazdayasna is both the religion of choice and the religion of truth (whether you call yourself a Mazdayasni or not).
Mazdayasna is not permanent anymore than Truth is permanent. Wherever Truth goes, Mazdayasna goes with Truth (because Truth is what Mazdayasni worship!!!). Which is precisely why we can not fix Mazdayasna within a book anymore than we can fix Truth within a book of science.
But what we can fix is what is not true. Santa Claus does NOT live on Greenland. And that we can fight against, intolerantly, as to save Truth and the Tolerance Truth requires to thrive.
2008/7/28 Parviz Varjavand
This I ask You, tell me truly, Lord.
How does serenity come to those
to whom, Wise One, Your religion is taught?
I recognize You to be the beginning.
All others I consider mental repugnants.
Summary Substance: Zarathushtra asks to be sure that serenity and tranquility come to those who have learned the best religion, the one which promotes the living world. Considering all the points mentioned in the preceding stanzas of the song, Zarathushtra recognizes Mazda, the Super-Intellect to be the beginning. All other conceptions of god/gods are seen by him as strong mental antagonism.
Pondering Points: Best religion brings peace of mind and matter. Intellectual mind sees Super-Intellect as foremost. Inconsiderate thinking breeds harmful fancies.
What am I supposed to learn from this?
That the religion that Zarathustra brought is the best and all that other religions belive in are "Mental Repugnants". I find this kind of thinking rather repugnant if I may be bold and say so.