Polyamory and Identity
Suppose I take myself to be in love with a single person but in reality there are two people that are the recipients of my affection. What I think to be one person is really a pair of identical twins; they have just never disclosed this fact to me. I am polyamorous de re but not de dicto (I might even deplore polyamory). But suppose that one day I discover the true state of affairs, much to my surprise and dismay. What should I do? How should I feel? I could decide to stop loving both of them, perhaps because I disapprove of polyamory; but then I would have to reject a person I genuinely love—two of them in fact. I could decide to keep one and reject the other, but on what basis could I make this decision? They are indiscernible to me, holding equal places in my heart. It would be irrational and unfair to prefer one to the other. So I seem left with the option of keeping both: allowing de re polyamory to become de dicto polyamory. It is difficult to see how I could be criticized for this decision, and I myself may come to be reconciled to it as time passes. So long as my two loves desire it too, polyamory seems the way to go.
For another case, suppose that I take myself to be in love with a single person but this person likes to adopt a different persona at different times. On Mondays, Wednesdays and Fridays she likes to present herself in a certain way (hair, personality, even bodily appearance), while on the other days she adopts a different mode of presentation. I am happy with this arrangement since it provides some welcome variety in the relationship. But it turns out that again there are really two people involved—I have been fooled. What should I do? I don’t want to reject both, since both are beloved. Should I reject one? This time I am not faced with the problem of indiscernible loves: and I might actually prefer one to the other. After diligent reflection I decide that I do prefer one to the other, so at least I have a basis for discrimination. But that doesn’t settle the matter because I do genuinely love both (and both love me). Again, it would be unfair to reject the marginally less beloved one, and I would certainly miss her. So I decide to keep both. All I really have to do is judge that two people are involved where once I thought there was one; otherwise I just keep feeling the same way. It is hard to see how I could be criticized for this decision. True, they shouldn’t have deceived me, but perhaps they had their reasons.
Here is a third case. My wife travels a lot for work, so I don’t see as much of her as I would like (suppose she feels the same way about me). We hit on an ingenious solution: she undergoes brain bisection and relocation of the two halves of her brain in separate bodies—that way when one half is traveling the other stays home. Maybe the bodies are indiscernible; maybe they are not. Granted that the resulting individuals are two in number, I am now in love with two people. I have entered a polyamorous state. Suppose that my wife (wives) and I are happy with the new arrangement and have no wish to return to the old monogamous state. It is hard to see how we could be criticized for our actions and feelings. If you think there is an undesirable asymmetry in our romantic entanglements, feel free to embellish the story so that I also undergo brain bisection and become two people; then each of us has two romantic partners where once we had one. This works for us, allowing us to provide ceaseless companionship to each other, as well as enhancing the family finances (maybe our children also benefit from having four parents). If this kind of thing became the norm, then elective polyamory would no doubt become socially acceptable. If the birth rate dipped too low it might even be encouraged (or mandated) by the government as a way of expanding the population. A religion might spring up extolling the virtues of this type of extended family. It is a way of doubling the love. It might even reduce the rate of divorce. 
These reflections should serve to lessen the taboo on polyamory.
 Polyamory has nothing to do with promiscuity; indeed, its existence might well militate against that form of sexual life. Adultery will be less of a problem in a society in which brain-bisected plural marriage is normal. (Of course, there is no logical reason why brain bisection could not create even more romantic partners.)