Do you have a source for this point?
It is pretty well established that the institution of pederasty was at its high point of acceptance during what is generally considered the greatest period of Greek civilization - from the battle of Marathon to conquest by Alexander. Perhaps the greatest of all Greek generals, Epaminondas, created the institution of the Sacred Band, 300 openly homosexual lovers whom he used as shock troops, very successfully, I might add.
Homosexuality in Rome was probably most accepted during the first two centuries AD, with several Emperors such as Calugula and Hadrian being very open about their practices. This period has generally also been considered the high point of the Empire by most historians, with Gibbon only one of a very long line.
After this period, acceptance decreased, with the Christian emperors instituting the death penalty for sodomy, burning alive if I remember correctly.
Unlike some homosexual activists, I do not claim that the open acceptance of homosexual practices caused these civilizations to peak at this time. Correlation does not equal causation.
However, if homosexuality being accepted = automatic decline and fall, you sure can’t tell it from the history of these two cultures.
Caligula and Commodus are two flaming examples of bisexuality and bad government.The empire collapsed several hundred years after these guys, often used as examples of the horrible nature of homosexually dominated governments.
OTOH, Hadrian was apparently a confirmed faggot and he is generally accepted as an excellent emperor.