This answer is an antithesis of Franklin Veaux’s answer, which I find unhelpful. I find his answer boils down to “because the West is right about sex”. And that’s not an explanation of “Why is the West so open about sex?”:
Because, through long experience, we have learned that societies are healthier, more egalitarian, safer, more fair, and more just when their members are open about sex.
(Who’s we? The contemporary West has, and South Asia or East Asia has not? Because what, the West is better? Wiser? More experienced? And yes, the West cares whether a society is more egalitarian or safe; that is not a universal value.)
Being closed about sex cloaks sex behind a veil of secrecy and shame. And when you treat sex with secrecy and shame, people suffer.
(The West has been an exemplar of treating people well, without secrecy and shame? The West has attained the pinnacle of righteousness, that the rest of the world strives for?)
I mean, you can believe all that. Hell, most of the time, *I* believe all that. But that’s hardly an answer to the question. Why the West?
Well, first of all, it was not ever thus. The West has waxed and waned about how open it has been about sex: the Elizabethans more than the mediaeval, the Victorians less. The Sexual revolution was foundational to the current Western openness about sex; and it was not a divine spark of inspiration that favoured only the West, it was an outcome of particular social pressures that converged by accident in the West.
And it’s not me saying so, it’s Wikipedia:
- Mitigation of negative consequences of sex
- Mitigation of sexually transmitted diseases, e.g. syphilis through penicillin
- Mitigation of risk of pregnancy: the pill
- Female empowerment: feminism, increased availability of employment and education to women, particularly in the aftermath of WWII
- Secularism in the West, reduction in the role of the Church in enforcing morality
- Urbanisation in the West, reduction in the strength of family as an enforcer of values. (When that happened in Venice after the Black Death, their reaction was to empower their Vice Squad to enforce sexual values: see The Boundaries of Eros. The Modern West tried that too, but failed.)
- Questioning of traditional values prominent in popular culture, e.g. by Freud
- Demographic change: the Baby Boomers’ strength in numbers
- The mass media, circulating notions of sexual freedom more effectively than in the past
The Sexual revolution combined with some foundational attributes of Modern Western culture that Franklin presupposes, but that need to be made explicit:
- Individualism against collectivism
- Eudaimonistic notions of the common good as rooted in individual happiness
- Notions of public health overriding “moral health”: science and medicine rather than morality guiding public policy
Most of these are particular to the West. And it hasn’t gone smoothly and inexorably, and there’s a lot of reaction to it, particularly in America. But the confluence of factors has been a Western confluence, not a global confluence. Hence, the West is more open about sex than other parts of the world.