There are significantly more "out" homosexuals than there were in 1850, even if you think homosexuality is purely orientational. Since we're talking about observed behaviour and not personal preferences, social consequences are highly sensitive to social determinations.
That aside, I sincerely doubt this (or sexuality) for that matter, is purely orientational. Consider a very undesirable man who is somewhat inclined towards polyamory in his youth. Because he is undesirable, he's going to have an extremely difficult time actually practicing polyamory. The result will be rather heavy, continual negative feedback. If he tries monogamy, and is relatively successful, he may start to lose interest in polyamory due to the fact that the rewards he is receiving contradict it. A more desirable man may have met with more success, gained positive reinforcement of polyamory, and decided to incorporate it into his identity.
For a non-sexual/romantic analogy, consider the same child born to two different families (or identical twins, if you prefer): a highly functional, wealthy family that strongly encourages him towards "traditional" success of whatever form best fits his skills, and a similarly functional but relatively poor family that encourages him to do whatever his father did and be self-sufficient. If we interview these two children at 21, we expect them to be very different people. They will likely both have very different but firmly held views on what constitutes a good life and what constitutes success, such that each might be miserable in the other's life. This is very much analogous to an orientation, as it is unalterable and not directly in the control of the individual. It is, nevertheless, highly sensitive to local social values and rewards. Some individuals are such that, almost irrespective of their circumstances, they will turn out a certain way - some underprivileged children will find ways to be lawyers and investment bankers, even with inhospitable childhoods, and some children of extremely successful people will regress to the mean despite their parent's every effort, in many cases quite willingly.
Many of us are familiar with Donald Rumsfeld's famous (and surprisingly useful) taxonomy of knowledge:
But this taxonomy (as originally described) omits an important fourth category: unknown knowns, the things we don't know that we know. This category encompasses the knowledge of many of our own personal beliefs, what I call unquestioned defaults. For example, most modern Americans possess the unquestioned default belief that they have some moral responsibility for their own freely-chosen actions. In the twelfth century, most Europeans possessed the unquestioned default belief that the Christian god existed. And so on. These unknown knowns are largely the products of a particular culture; they require homogeneity of belief to remain unknown.
By definition, we are each completely ignorant of our own unknown knowns. So even when our culture gives us a fairly accurate map of the territory, we'll never notice the Mercator projection's effect. Unless it's pointed out to us or we find contradictory evidence, that is. A single observation can be all it takes, if you're paying attention and asking questions. The answers might not change your mind, but you'll still come out of the process with more knowledge than you went in with.
When I was eighteen I went on a date with a girl I'll call Emma, who conscientiously informed me that she already had two boyfriends: she was, she said, polyamorous. I had previously had some vague awareness that there had been a free love movement in the sixties that encouraged "alternative lifestyles", but that awareness was not a sufficient motivation for me to challenge my default belief that romantic relationships could only be conducted one at a time. Acknowledging default settings is not easy.
The chance to date a pretty girl, though, can be sufficient motivation for a great many things (as is also the case with pretty boys). It was certainly a good enough reason to ask myself, "Self, what's so great about this monogamy thing?"
I couldn't come up with any particularly compelling answers, so I called Emma up and we planned a second date.
Since that fateful day, I've been involved in both polyamorous and monogamous relationships, and I've become quite confident that I am happier, more fulfilled, and a better romantic partner when I am polyamorous. This holds even when I'm dating only one person; polyamorous relationships have a kind of freedom to them that is impossible to obtain any other way, as well as a set of similarly unique responsibilities.
In this discussion I am targeting monogamy because its discovery has had an effect on my life that is orders of magnitude greater than that of any other previously-unknown known. Others I've spoken with have had similar experiences. If you haven't had it before, you now have the same opportunity that I lucked into several years ago, if you choose to exploit it.
This, then, is your exercise: spend five minutes thinking about why your choice of monogamy is preferable to all of the other inhabitants of relationship-style-space, for you. Other options that have been explored and documented include:
These types of polyamory cover many of the available options, but there are others; some are as yet unknown. Some relationship styles are better than others, subject to your ethics, history, and personality. I suspect that monogamy is genuinely the best option for many people, perhaps even most. But it's impossible for you to know that until you know that you have a choice.
If you have a particularly compelling argument for or against a particular relationship style, please share it. But if romantic jealousy is your deciding factor in favor of monogamy, you may want to hold off on forming a belief that will be hard to change; my next post will be about techniques for managing and reducing romantic jealousy.