I think he is saying that people who live comfortable, sophisticated lives tend to think that those who live simpler, more rural lives are happier. The "citizens of the capital" are the potential market for a film about a natural, "unpolished" Asian girl living in the jungle - they would see her life as somehow purer, more real than their own. The irony is that the girl's "simple" existence has made her very ill - Enright was very aware of poverty and had spent a lot of time in Asia. Hope this helps for a start.
