Duty premise: if you think that talking about sex or sexual revolution is not relevant to the future, you are wrong.
Many of the current answers to the question "why do we have sex?" are obvious: most of them include the need for reproduction. Sex is (still) the main way of giving birth to children.
But how would our approach to sex change if it no longer had to do with procreation?
We do it to reproduce
Since the birth of the first "test tube baby" over 40 years ago, millions of terrestrials were born thanks to this method. The number is destined to grow in proportion to the improvement of tools capable of identifying genetic risks in embryos.

"I foresee that in the future people will still have sex, but not for reproductive purposes": is the prediction (shock?) of Henry Greely. In his book "The end of sex and the future of human reproduction"the author speculates that in an inclusive period between the next 20 and the next 40 years all those who have good health coverage will prefer to conceive in test tubes.
Greely's book explores the ethical and legal challenges behind this change. "As for similar things there will be a first negative reaction, but gradually it will be tolerated and then preferred".
In a world where children are made in the laboratory (perhaps even in artificial womb), and the "old style" reproduction with more and more risks is destined only to the most disadvantaged classes, what new meaning does sex assume?
On the biological level there is an obvious motivation for human sex: we do it to procreate and spread.

This rule was introduced by a particular interpretation of the sacred texts of the Christian tradition (actually in the "Canticle of Canticles"also refers to passionate, erotic and wild sex between two lovers, it is not specified" wife and husband "). It is an "ethical" type of sex that has been sublimated by heights of pure poetry in St. Augustine and has great influence especially in the West. According to this scheme, sex is "ethical" if it is practiced primarily to reproduce.
We do it to be loved
Another "why" to sex comes directly from Aristotle, who in his own Principi introduces a syllogism: “Being loved is preferable in the relationship, based on the nature of the erotic desire. Erotic desire is more a desire for love than a sexual relationship. If it is above all for that, this is also its goal. Either sexual intercourse, therefore, is not an end at all or it is, but it is for the sake of being loved. "
For Aristotle, in short, it is not love that points to sex, but the opposite.

Like many, the Greek philosopher assumes that Love and Sex go hand in hand, but he never tried to prove this assumption. He merely says that sex "is not the ultimate goal of erotic desire". In other words, if Aristotle is right, sex would not have an erotic purpose. Sex wouldn't be about sex.
In short, why do we do it?
To procreate, of course. To join us, sure. But they are only two of the possible answers.
Think about the food. Eating in groups for our ancestors was linked to survival: food for the group equals food for the individual. Today we take pictures of food, eat absurd sandwiches and other things that no longer have a real connection with survival. This also works for sex. It causes us pleasure and sometimes we do it only if it doesn't make sense, only if it brings a mere satisfaction.
Maybe it's time to admit it: to enjoy it's the main reason we have sex. Oh God, we may not admit it, but the sexual revolution will come anyway.
The pill
There is a profound reason why 1968 is remembered by all as the affective center of a sexual revolution. It is the year of the pill, a small drug that has had the effect of an atomic bomb.
In a 2015 research Jean M Twenge, professor of psychology at San Diego State University, examined the sexual attitudes of Americans from the 70s to 2010. His laconic conclusion: "Americans have willingly accepted non-marital sex."
Habits change, the approach to sex is further away from the bonds, our sex ethics evolve, often faster than society.
What is natural and what is not?
Hard to say. Of course, many of the traditional ideas about sex are quite incompatible with nature. Take homosexuality: some say it is an unnatural fact, because for example animals would not be homosexual.
Nothing could be more false. Japanese macaques, fruit flies, albatrosses, dolphins are just some of the 500 animal species that also include homosexuality.
Of course, animals don't "consider" themselves gay. They don't even "consider" themselves straight. They just don't define themselves based on what kind of sex they have.
By this I am obviously not saying that gay sex has no purpose or meaning: he has many, including love.
Certainly, historically, gay culture has also been increasingly open to the idea that sex does not necessarily have to have social and conformist obligations, and that it does not need them. This freer approach could even be among the inspiring reasons for certain prejudices against homosexuals.
The "ethical scheme" of heterosexuals contradicts itself. The vulgar accusations of amorality aimed at gays are not taken into consideration when a heterosexual engages in the many sexual activities that do not find an outlet in procreation.

Matter of time
Thanks be to God (or whoever for him, Lucio Dalla would say) the preconceived hostility towards homosexuality continues to decline all over the world, net of the complaints that rightly make and must make noise.
A Williams Institute study at UCLA Law School observed the changing attitudes of people in 141 countries around the world. In 57% of these countries there is a great growth in the general reception and acceptance of the LGBT world from 1981 to 2014.
It's not all roses and flowers, of course. The researchers note that while the biggest increases are recorded in the countries considered most tolerant (Iceland, Holland, Sweden, Denmark, Andorra and Norway), the most refractory nations (Azerbaijan, Bangladesh, Georgia, Ghana) have further radicalized. However, the general picture improves.
Media models
There are many reasons for this increase in tolerance: public support from medical and psychological associations, positive media coverage (in pop culture more and more examples of homosexual love are represented) and not least the personal knowledge of those who come out. Hard to think that gays want to "destroy civilization" when they are your sister, your piano teacher, your florist, the volunteer fireman who lives across the street.
The LGBT people as a pioneer of the new sexual ethics
LGBT culture is offering the world new avenues to reflect on the ethics of sex, in ways that do not necessarily oblige procreation, marriage or monogamy. A 2005 survey shows that 40% of gay couples live an open relationship against 5% of straight people: if this type of experience becomes the general norm, it will have been the gays who have driven the new sexual revolution.
What do straight people say?
I imagine more than a few heterosexuals will turn up their noses, but it's hard to say today that heterosexual morality has any moral or ethical authority on the subject. Modern popular culture now shows us many models of dysfunctional heterosexual relationships, marital and otherwise. The "traditional family" never shows as today that it has many difficulties in teaching something on the subject of coexistence.

The tools (and standard bearers) of the revolution
Over the years, many futurologists have launched into predictions about the future of sex. From VR porn to sex with artificial intelligenceand at our Sexbot to remote sex the future seems more digital and less organic also in this field.
While the future will bring us technological changes, however, the sexual revolution will be driven by new ideas.
We will rethink procreation
Since 1978 more than 10 million children worldwide have been born with in vitro fertilization. A number destined to increase exponentially as treatments become more widespread and cheaper.
The world will approach an ethically and socially accepted form of eugenics. A couple wishing to have a child will visit a clinic, bringing sperm and skin samples. In one or two weeks she will be contacted to select which of the 100 embryos produced from their samples to choose for fertilization. The choice will likely be based on an accurate set of information relating to genetic heritage, disease susceptibility and other characteristics.
We will rethink monogamy and sentimental commitment.
Having a sexual partner for the entire adult life seems easier with a relatively low life expectancy. With the increase in life expectancy (from 1960 to 2040 the average life will be 25 years longer), things will change. According to many futurologists the first person who will live over 150 has already been born before 2001: how realistic is it to think that she should be limited to having for 100 years and only one sexual partner goes by? Divorces and second marriages are already on the rise today. With the higher life expectancy, "until death do us part" will stop being a prime target.
We will rethink sexual identity
If sex stops being necessarily associated with the procreative function, will sex become a mode of communication that is independent of genders? In other words, will the concept of sexual orientation and identity be linked to the notion of reproduction or will the words "homosexual" and "heterosexual" remain only in the history books, and will we live in a 360-degree "sexual" society?
If the new sexual revolution becomes more and more mass it will also be for the many LGBT people who for decades have been inviting "the dominant culture" to rethink its sexual ethics.
Sex will always have its own meaning and purpose, but it will be more for someone than for something. It will be for those who do it, first of all, for the joy that allows people to meet, to unite, to experiment.