The most basic tenant of nature and all creatures is that they reproduce so that the species keeps going and evolution happens. Without this, most of existence would be devoid of any life like most planets in the universe (at least, as far as we know). Almost every creature on earth reproduces in an instinctive manner where the act of forming a new life is just done as an act in and of itself. Once completed and an offspring is born, hatched, or grown, a basic set of rules govern survival of the young and then they are left to fend for themselves. Turtles laying eggs closer to the water so that newborn have a chance to escape before being eaten is one example. Or the seed of a plant having a hard or in some cases poisonous covering to protect the replication material inside is another example. Very few creatures form any sort of bond with their offspring and in most cases don't even recognize them. Dogs are the most common example of this lack of attachment or recognition of their offspring after a very short amount of time. Most reptiles and fish have none of either and often eat or mate with their offspring. Elephants and Orangutans are two of few examples where there is a strong bond between the mother and her children, but these are exceptions to the rule.
Because Nature wants and requires reproduction, she has designed mechanisms to encourage this. Hormones, especially in females, provide the drive and impetus to have sex which leads to reproduction. All of this is done on instinct and the entire process is basic and elemental. The one creature that stands poles apart with regards to sex is humans. While we have the same instincts, hormones, and drive for sex, it has been layered with so many complications and dimensions, that the original goal of reproduction has been completely sidelined for something altogether different and probably unintentional, at least from Nature's standpoint. One primary driver for this is that the type and dimension of pleasure that the journey to orgasm and the orgasm itself brings to humans is very unique and is mirrored for both sexes in almost equal measure. This is also why masturbation is so common among humans (and some primates, our closest relatives) while almost no other creature in nature does this. In fact, few creatures in nature have sex for pleasure versus it being an instinctive act much like peeing or eating. Bonobos, considered the world's most intelligent animals and closest human relative, have sex for pleasure including same-sex partners. Farther from humans, dolphins and giraffes also engage in sex for some level of pleasure.
Sex is just a natural thing that all creatures, including humans, are endowed with for reproduction. At a young age, to drive people to have sex to procreate, the body generates hormones to increase the drive for sex. This is why teenagers are obsessed with sex and it is always on their minds. Before puberty, it was irrelevant what somebody’s body looked like and their reproductive organs did not matter. We were simply kids who were having fun and doing what kids, male or female, do. But as soon as puberty hits, our minds get hijacked by hormones and sexual drive becomes the center of one’s focus. The small physical differences all of a sudden become a world of their own and take over much of your world at the same time. Beyond these differences, there is no real man or woman, and we are just human. It is only on the physical level of the body is there such a distinction. To promote reproduction for the species to carry on, there are also small physiological differences. To support those differences, there is a certain psychological mechanism. Everything else like the eyes, nose, legs, heart, etc. are the same and nearly identical.
One thing that I cannot fully answer is why nature gave man such a significant and asymmetric experience of pleasure with sex and not to almost any other creature? Some have speculated that our Creator wanted us to be able to touch the divine realm via a physical act and that sex was the result of that. Regardless of the reason, this level of pleasure has caused us to do something that has led to the original goal of reproduction to become an afterthought and altogether optional. After all, 99% of sex humans have today is not with the goal of reproduction but rather, pleasure. But why is it so wrapped up in taboo and most find it difficult to discuss openly? Why do religions ban sex before marriage? Why can it not be discussed openly and with ease like the weather or the economy? To me, the reason for all this is that we allowed the process of sex to enter the mind vs. keeping it to what it is… a purely physical act that comes with great pleasure but can also lead to reproduction. The mind is magnitudes more complicated and multi-dimensional than the body and provides a nearly unlimited means to modify the experiences of sex. These can range anywhere from casual sex between strangers to more complex things like prostitution (the world's oldest profession) and far darker things such as pedophilia. By putting sex into the mental realm, we have encased a basic physical act with our unlimited mental capacity of imagination. We have taken the physical act of sex and transformed it to the mental dimension of sexuality. This has also caused the small physiological differences to be magnified and they became “something” in the mind. Thus, a significant percentage of our energies in modern society is either spent thinking about sex, avoiding thinking about sex, or punishing oneself for thinking about sex. I also propose that lust as a device did not really exist until sex entered the mental dimension and became magnitudes amplified by imagination and fantasy. Desire and drive are all that is necessary for sex as a procreative function, but lust is an altogether different dimension that exists solely in the mind. It is the single force that is responsible for untold atrocities such as child molestation or rape where the ones committing these acts claimed to have been "driven blind by lust".
The mind of man has created so many complexities and contradictions that it is no wonder than our collective mental tribulations and angst around sex is infinitely more than our physical ones. For example, most religions mandate there is no sex before marriage and that we have to be with a single sexual partner our entire lives. Yet Nature (or the same God of said religions) has imbued us with insatiable drive to procreate and attached a significant bonus of pleasure to do so. But, since we long abandoned sex-for-procreation only and traded it for the far more lucrative sex-for-pleasure, there is no way a single partner or single mental dimension can satisfy the infinitely possible creations of our imagination. The Internet, along with the manifestation of imagination through pornography and sexual motifs, supercharged this imagination to a level most could not imagine even a few years ago. This has significantly accelerated where humanity was headed anyway, which is the complete commoditization of sex and reduced to an act of attracting a sexual partner by "swiping right" on your phone. Is it any wonder that the younger generations have a very blasé view towards sex and don't attach much meaning to it? Or that most explore the dimensions of sex via pornography? Ironically, they have reached the other side of the coin where the mind has put sex back to where it was to begin with… a purely physical act without any of the nonsensical mental constructs attached to it. The ultimate travesty is when love or the expectation of love is attached to sex. The untold suffering of anger, sadness, and depression that has come from this attachment is a very sad state of affairs.
My personal view on sex is that if you feel it is right and your partner is 100% consenting, there is no reason to not do it. We were given the added bonus of significant pleasure for this act of procreation and no reason to waste it, even if we don’t want to do it to procreate. This is also why I believe that sex education should be taught to every young person and the risks such as disease identified early on. There should also be psychiatric education on the mental impacts of sex and students should be told to not attach any mental constructs to it. The old adage of "if I have sex with him, he will love me" should be destroyed and kids told that it is a purely physical act and should be treated as such. This is also why I am a big proponent that masturbation should also taught during sex education and encouraged as a viable alternative to having sex with a partner. It is sad that the biggest organized religions in the world vilified sex and made it a taboo to talk about these things. Thankfully the Internet + Smartphone revolution has obliterated this wall and kids have all the knowledge they need in the palm of their hands. And not only knowledge, but all the tools to find a willing partner with just a few swipes on an app. But, in my opinion, an open an honest education from medical and mental-health professionals is a FAR better path than learning from PornHub. I also think governments of the world should legalize prostitution and put in all the health and social controls to ensure workers are treated with respect and work in a safe environment. This has been done with great success in Amsterdam and other parts of Europe. It is well beyond time to stop being enslaved by dogma and deal with sex as a natural and physical part of life. If we can just learn to keep sex in the physical domain and not turn it into sexuality in the mental domain, we would all be much more peaceful and happier. And a lot of the darker aspects will reduce as many of those are caused by the repression of a natural, physical need.
There is another dimension of sex that is, as expected, completely misunderstood in the west which in Tantra. It is commonly thought of as uninhibited sex but that is a complete misinterpretation. The word itself means a technique or technology and is used in the context of our energy body, that which our physical (accumulation of food) and mental (accumulation of memory) bodies are housed within. The technique of Tantra Yoga is to go beyond the limited experience of the body and mind and use them as a stepping stone to higher dimensions. The Tantric path is not about sex or sexuality but because people want a justification for both, they use Tantra as an excuse. There are two pathways in Tantra, a left-handed one that is crude and ritual-based and a right-handed one that is more internal and energy based. In the left-handed path, there are certain rituals that include sexual functions (not sexuality) and that part was perverted to write books, sell classes, and have all manner of sexual acts, all in the name of Tantra. This is utter nonsense and has nothing to do with Tantra as a practice. The goal of Tantra is to enable one to use their energies to make things happen. Sharpening your intellect, being able to lift very heavy weights or run ultra-marathons, or become a very loving person, all are considered Tantra. The goal of Tantra is to deliver the practitioner to a higher dimension of consciousness, not trap them into the compulsive nature of sexuality. This process is definitely orgasmic but not sexual. Yogis who have reached this state have every cell in their bodies and mind dripping with orgasm but with no motion or physical action.
Finally, I also wanted to touch on homosexuality and sex between partners who either can’t become pregnant or choose not to via contraception. To me, sex was our Creator's way of getting us to reproduce and as an incentive, pleasure was added to the process. While I still don't quite understand why the level of pleasure is so significant, I still do believe it was the incentive to has sex for procreation. In that sense, homosexuality is a dead end for procreation and does not serve the purpose for which sex was designed. I also have no kids, so I (and my wife) are also genetic dead ends, so I am not making this comment in any negative manner but rather just stating a fact. But, since there is such a level of pleasure associated with the act, it makes complete sense why homosexuality not just exists but thrives across the world. I think it is beautiful that two (or more) people, regardless of their body parts or identity, can enjoy the immense pleasure associated with sex without worrying about the procreation aspect of sex. This is also why I am not surprised by the existence of the many darker (for most of society) realms of sex as the mind is capable of immense levels of perversion. Our imagination is infinite and when we put sex in that dimension, who is to say what path one can choose to attain the pleasure associated with sex? In the end, if sex is done with the universal constructs of love and kindness, who am I or anybody to judge at any level if it is right or wrong? We do live in an existence that is comprised of infinite (not just 50) shades of grey after all.