So wait, he's advocating abandoning one religion to accept an older one that came from the same country? Why not simply abandon the mental bondage of religion altogether?
Maybe because humans don't function like that, at least till date have never been like that. We can't figure out our relation with the world until we properly define ourselves, until we find satisfactory answers to the question of "Who am I?" we can't relate to the world around us. Even in countries' like Norway or Sweden, where a large % of the population disbelieves in God, you can see people in Lutheran Churches in Christmas, babies are most often baptised even if born out of wedlock, & there remains a lingering attachment to the Christian Lutheran faith.
Iran, on top of that is a relatively poorer nation, & Islam is for them religion, ethical basis & cultural heritage. If Islam is removed, there's bound to be a big hole, in their societies & hearts, which can be filled by the other biggie, Christianity or by Zoroastrianism which is rooted to their soil.
For an old & proud people like Iranians, to become Christian might seem like becoming Western, to finally succumb to the very forces they waged their wars against.
And it will lead a lot of people like Sparky & Diotima to gloat, which I certainly won't like!!!
To become Zoroastrian, on the other hand, will give them a God, moral underpinnings & a sense that they still retain their age old culture,
they still remain different-distinct.
And Zoroastrianism doesn't require jihad, nor does it require its followers to hate Jews, the Zorosatrians were Zionists when they gave the Jews their lands 2600 years ago, so it could well be a viable alternative, and a nice one.