WrongBot:

But the reason that inequalities of romantic and sexual opportunity go unquestioned is not due to a failure to perceive those inequalities. Rather, it's because there is no (ethical) way to systematically reduce them.

Whether or not monogamous societies are more egalitarian than sexually laissez-faire ones, coercing one into the other would require a reduction of basic freedoms that I find unacceptable.

What about reductions of freedom that don't stem from any legal compulsion or violent threats, but merely from social norms enforced via status and reputation (and, obviously, their consequences on people's future willingness to maintain and establish various sorts of private relations with you)? Do you believe that these are also unacceptable?

If the answer is yes, then you must perceive any realistic human society, including the one you live in, as a hell of intolerable suffocating constraints. (Honestly, I would lie if I said that I don't feel a certain sympathy with this perspective -- but people are often biased in that they make a big deal only out of certain constraints that bother them, while completely overlooking other even more severe ones that they're OK with.)

You also seem to be operating under the assumption (and I apologize if I'm reading too much into your comments) that such a free market would necessarily involve successful (or possibly "high-status") men attracting the vast majority of the pool of available women, leaving few options for less successful/attractive men,

That assumption is, in my opinion, indeed correct, and consistent with what we observe in reality. But I don't see why you think that I was talking exclusively about men. Less attractive women also get a bad deal in a society where attractiveness is an important status marker, which I see as inevitable under sexual laissez-faire. Moreover, those women who would like to form permanent monogamous relationships, especially if they're less than stunningly attractive, are faced with much worse prospects in a situation where any man they attach themselves to could be at any moment tempted to defect and try his luck playing the field a bit more before settling down. (Again, note that I'm not contrasting this with a situation where the man would be somehow coerced into attachment, but with a different state of social norms where this would simply be a less attractive option.)

Now, you write:

which ignores the ability of women to form multiple attachments themselves, as well as relationships in which all partners have multiple attachments, which more closely resembles the polyamorous ideal.

But this seems to me like fallacious reasoning. You apparently assume that if women are to form multiple attachments, there will be more attachment opportunities for all men, not just those in the upper tiers of attractiveness. Yet in reality, we see some contrary evidence, in that when women become more promiscuous, the additional amount of sex taking place is not at all distributed randomly or equally across all categories of men; instead, those in the upper tiers of attractiveness get the overwhelming part of it. (I know that this is not equivalent to what you have in mind, but I do think that there is enough similarity to provide at least some relevant evidence.)

Furthermore, I think that the idea of "sexual laissez-faire" that you are discussing here is something of a non-sequitur. No one has suggested that we adopt anything of the sort as a cultural norm; I should note that polyamorous standards include levels of honesty, communication, and egalitarianism that are not at all compatible with any kind of "free market."

You seem to imply that under your most favorable social arrangements, there would be some constraints relative to a complete sexual laissez-faire (even one with the usual caveats about consenting adults etc.). But how would these be enforced? Or do you believe that people would spontaneously follow them under some favorable circumstances?