Borderline Racism?
It is disappointing to see some comments here, along the lines of Iranian = "potential terrorist" or Asian = "less than competent". What plausible reasoning is there for an Iranian to blow up a Malaysian/Chinese flight?
State Actors: Far more violence is perpetrated against Iran by the West (including targeted assassinations of civilians) than by Iran. Furthermore, why would they take action against an ally?
Non State Actors: the primary NSAs in Iran are Sunni Baloch nationalists/separatists. I can see why they might attack an Iranian, Afghan or Pakistani plane, but it is a huge stretch to think they would put serious effort into attacking a far harder target with no obvious benefit to themselves.
Even terrorists need to have reasons, even if the media like to pretend otherwise.