Two words have been let loose on society by an artist who, for better or worse, may find the rest of her life and career inextricably bound up with them, “vagina” being one and “taboo” the other. The artist herself needs no introduction. She is (or briefly was) the most famous woman in Japan, thanks primarily to an aborted (and almost incredibly stupid) arrest for alleged obscenity.

Whether or not Megumi Igarashi, aka Rokudenashi-ko (“no-good girl”), was the first ever to discover that the vagina is shaped something like a kayak (or vice versa), she certainly broke new ground in building a kayak and calling it art on the basis of that resemblance. (The obscenity charge had nothing to do with the artwork per se; it arose from her fundraising technique of rewarding donors with data enabling a 3-D replication of her vagina.)

Anyway, the word “vagina,” along with some less genteel synonyms, is no longer “taboo” in Japan, as numerous commentators here and abroad have hastened to assure us. It was rather silly that it should have been in the first place, and what this episode proves above all is that nothing combats silliness more effectively than silliness, both the artwork in question and the arrest that followed fitting the bill admirably. Perhaps from now on the vagina will be regarded as Rokudenashi-ko says it should be, as simply “part of the body … no different from arms and legs.”

Why hasn’t it been? Or, to phrase it in Rokudenashi-ko’s terms, “I don’t understand why my vagina is considered obscene.”

Police bungling has unfortunately made that the question of the day, but a better question might be, why is it considered taboo?

It’s better because it takes us farther. It invites other questions: Why is anything taboo? Why is anything forbidden? Why are (or were) “private parts” private?

Sigmund Freud, in “Totem and Taboo” (1913), stresses the arbitrary nature of taboo: “Taboo prohibitions have no grounds and are of unknown origin.” Taboos are “the oldest human unwritten code of laws. It is generally supposed that taboo is older than gods and dates back to a period before any kind of religion existed.” The point seems to be that even the most primitive human groups impose prohibitions on themselves, rational or (more often) not. They say to themselves, “Thou shalt not.” Why?

The most famous taboo story of all is the ancient Greek myth of Oedipus, the king who unwittingly married his mother and had children by her. It’s the source of Freud’s Oedipus complex. What’s the big deal? Oedipus didn’t do it on purpose. It was an honest mistake. Why didn’t he just shrug and say to Jocasta, his wife-mother, “What the hell, no harm done — a bit gross, I grant you …” But of course harm had been done — their city was dying of plague, and the incestuous marriage was its cause.

That’s silly to us — we don’t think like that any more. But some ancient taboos are more congenial to modern thinking. The Ainu of Hokkaido, a most unwarlike people, nevertheless in the 17th century fought a war against Japanese gold miners who, in violation of Ainu taboos, were wantonly polluting the rivers. Historian Sarah M. Strong, in her book “Ainu Spirits Singing” (2011), links the taboo against pollution to another taboo against contact with menstrual blood. Convoluted indeed are the impulses of human nature before it gets “civilized”!

Be that as it may, Ainu bows and arrows were helpless against Japanese guns, and pollution won, with consequences we’re still living with.

Modern, rational, scientific life is fatal to taboos — to most of them, anyway. Exceptional are the strangely durable taboos surrounding female sexuality. Liberation in the West began in the 1960s; in Japan, somewhat later, proceeding more slowly in proportion. Today it lags rather far behind. The women’s weekly Shukan Josei ran a piece last month on “women who buy sex.” Men, of course, have always bought it, and who cares? Their wives, maybe, but that’s their problem.

Japan’s fūzoku (erotic entertainment) business is worth an estimated ¥2.3 trillion annually. Until recently patrons were exclusively male. Women, Shukan Josei says, were presumed to feel desire only in connection with maternity. Debunking that conventional wisdom were the liberated women of the 1980s. What set them free? Money.

Japan’s economy back then was really something. The bubble swelled and swelled, before finally bursting in the early ’90s. The young women of the bubble era didn’t hide their desires, they flaunted them and satisfied them — as many continue to do today as middle-aged women, freer than their mothers and grandmothers ever were, which goes without saying, but also freer than their daughters, children of the straitened, straight-laced post-bubble stagnation.

The result, as Shukan Josei shows, is a new branch of the fūzoku industry, catering mainly to middle-aged women and typified by establishments such as Tokyo’s Black Swan. The entrepreneur behind it — it opened in June last year — is adult-video star Yoji Agawa, who in 14 years has appeared in some 6,000 films and who now, backed by a staff of 10 fellow AV actors, brings his experience to bear in the cause of a woman’s right to pleasure for pleasure’s sake — all the pleasure she can pay for, and it doesn’t come cheap. An average fee among the various “courses” is ¥40,000 for 90 minutes, in return for which, Agawa says, “We’ll do anything that’s not illegal!” Splat goes the last taboo. You’d almost have thought Rokudenash-ko’s battle was won before she enlisted.

Her arrest proved otherwise — just as her release six days later may be said to prove that society is moving, or lurching, in the right direction. Ah, vaginas! The weekly Shukan Post was reminded by all this of “The Great Wall of Vagina” (2011), by British artist Jamie McCartney. Imagine a wall — actually 10 panels — 9 meters long altogether, decorated wall-to-wall, so to speak, with 400 plaster casts of female genitalia!

“I included as broad a demographic as I could,” McCartney explains on his website, “with volunteers coming from all walks of life and ranging from 18 to 76 years of age.

“The thing about it is,” he adds, “it’s not erotic.”

That’s true, it’s not, and that’s it right there. You can disenchant the private parts — make them public, like arms and legs — but which weighs more heavily in an assessment of the result: the increased freedom, or the diminished eros?