I've actually thought about this before, and I think I have a decent reason why I think Iranians that grew up in the west are sometimes really self-hating. It's not really their fault completely. If their parents never bother to teach them their language and all that they really know about their country is what western media tells them, of course there is going to be issues. Add that on to most people in their host countries probably thinking less of their people, having negative stereotypes of them, that sort of thing likely plays a role as well.

Arabs at least have each other. Iranians really don't have anyone to rely on. Even Iran's own neighbors has many people that don't like them, and distinguishing between individuals and a country is something that for some reason is quite difficult for some people, so I bet that there is really a sense of isolation and hopelessness for some diaspora Iranians.

I think it would be interesting to study the mental health of Iranians living in the west, particularly in the US. I bet that a significant amount have mental health issues, some sort of psychological trauma, etc. But then again, I doubt anyone really cares.