Seriously, if you're a celeb over there and caught smoking a joint, your career is basically over.
Even the infamously prudish U.S. is more accepting of it.
I'm guessing it's a leftover of U.S, imperialism, like how all their porn is still censored.
Feudal Japan tolerated homosexuality and orgies, at least among the noble class. I guess somewhere along the way, they became hyper-prudish, but I'll let a more educated Japanophile elaborate on the reasons. What's strange is how morally conservative modern Japanese are, despite the very low rates of religiosity. And even those religions (Shinto and Buddhism) are much more permissive than the Abrahamic faiths.
A lot of it is leftover from the modernization period, when the Japanese ruling class intentionally affected as many European mannerisms and attitudes as they could.
But there was a second wave of cracking down on degeneracy when they went fascist. Much like West Germany, the US put a lot of the fascists back into power when they took over after the war - and it's not like MacArthur was interested in pushing back against it.
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You can look up an ukiyo-e painting of a woman fucking an octopus. It's not just a modern phenomenon.
Don't forget that "The Dream of the Fisherman's Wife," i.e. a woman getting eaten out by an octopus, was designed by Hokusai, whose "Great Wave" is probably the most well-knoen ukiyo-e print. It's generally argued that nearly all the famous ukiyo-e artists also did shunga (erotic pictures), and that something like 3/4 of all ukiyo-e prints in circulation were shunga.
At the same time, it was technically illegal to be making these things in the first place, since they had to be distributed without an official stamp from the government censor. So in Japan freaky shit and government censorship working hand in hand goes all the way back to the beginnings of modernity itself.
they definitely started out as a conservative feudal country before the hyperindustrial & military expansionist/fascist swing