Mara Hvistendahl argues that China isn't undergoing a sexual revolution; it's rediscovering its past:
Roughly half of the emperors of the Han dynasty (206 BCE–220 AD) kept young male lovers — a fact we know because imperial scribes dutifully recorded their affairs in works like Biographies of the Emperors’ Male Favorites. Such tolerance prevailed up through the Ming dynasty (1368–1644), when artists produced sex scrolls depicting intercourse between men.
It was only in the second half of the 19th century, as Western values seeped into China following the Opium Wars, that puritanism became more entrenched.
First, the rulers of the Qing Dynasty (1644–1911) made adultery a serious crime punishable by beating, imprisonment, or exile, and then the early leaders of the new Republic established by the 1911 Revolution continued the repressive trend. Later, in the first half of the 20th century, as Chiang Kai-shek’s Nationalists and Mao Zedong’s Communists battled for control of the country, the two organizations, though diverging on many issues, both conflated modernity and science with bodily restraint. At this time, [Richard Burger, author of Behind the Red Door: Sex in China,] writes: "A stigma emerged against unwholesome behavior — such as homosexual sex, patronage of brothels, or excessive sexual activity — as being backwards and feudal and not appropriate in the new social order." Mao took this notion to a new level after 1949, stamping out prostitution and mandating an androgynous, sexless style of dress, even as he himself maintained stables of mistresses.
(Image: Woman spying on male lovers, Qing-Dynasty, from Wikipedia Commons)