Michel Foucault does a really good job in History of Sexuality Part II of demolishing this idea. The Greco-Roman idea about sexuality simply did not take gender attraction into account as the primary determining factor of sexuality, while that's all that 21st century sexuality can think about. As in, there was a complex system of sexual morality in ancient Greece, but it was based on things like the Aristotelian idea of moderation and the Golden Mean: having too much sex, regardless of the type, would make you "debauched." Furthermore, there was an extensive bias against sexual relations between a pair of adult men, due to the idea that it was shameful or degrading to put oneself in that submissive position. Foucault argues that the ideas of flirtatious couqettishness and sexuality as a sort of commercial relationship where a powerful man would offer a boy a relationship in return for all sorts of social goods was merely transformed in later eras to a similar attitude for young women: in ancient Greece, for a boy to be "eager" or not "hard to get" was incredibly socially harmful to his career.
The main thrust in the 21st century seems to be against shame or "repression," (a trend he tackles in the first chapter of History of Sexuality Part I, the famed "We Other Victorians"), and the Greek model, which is just as much built on shame and repression as the Christian model, is not parallel to what people are trying to build. Furthermore, the 19th-century hangover of obsessive classification of sexuality in type is about as far from Greek mores as one could get.
This is a very good explanation.
