If there really is no problem, how does the Rabbi explain the enactment? Why was it accepted by the Ashkenazi communities? How does something completely permitted become forbidden, especially when there is nothing in the texts that explains the reason for the enactment at the time it was made (aside from reasons that were given only after the fact, centuries later!!!)?

I assume the basis of the enactment was various distortions that arose around the matter (I spoke about problematic effects). Some of them were probably not necessarily moral but social-religious (from a religious perspective it apparently seemed preferable to him to have a pair-bond of two). But even if Rabbeinu Gershom thought there was a moral problem here, I don’t agree. It is clear to me that there is no moral problem here if all sides agree wholeheartedly. But a prohibition does not necessarily depend on morality.
Not every enactment receives real-time explanations. Moreover, sometimes it is self-evident and doesn’t require explanation. In most rabbinic enactments, for example, there are no reasons given in the body of the enactment. To the point that some authors of works on legal principles wrote that when the reason does appear, the enactment may be interpreted in light of its reason (which is not what is usually done).

Polygamy is very harmful socially because it creates a zero-sum game between a few men who enjoy many partners and many men with no partner at all. As a result, phenomena such as homosexuality, sexual blurring, and sexual confusion spread on the margins of society, where lower-status males despair of finding a partner. It is no accident that the polygamous Sephardim were concerned about seclusion between males, while the monogamous Ashkenazim were not concerned about that at all.

Another problem is that instead of focusing on repairing the world, in a monogamous world, in a polygamous world people focus on attaining social status that will get them more partners. Thus, for example, in a polygamous society like today’s permissive society, people with status and tenure, such as professors in academia, tend to voice problematic and not necessarily logical views in order to mark themselves socially (the long tail of the peacock), and in that way attract young and beautiful female partners from among their students.

I disagree. First, you assume that sexual blurring and sexual confusion are moral problems. In my view they are not. Second, you assume that wherever social problems can arise, individuals should be restricted. With that approach you won’t get very far. Accumulating money also creates problems of chasing social status. So do sports competitions, and more.
The reduction you’re making of academic sensationalism is astonishingly shallow. I find it hard to accept that it’s done in order to attract young and beautiful women. By that logic, Haredi and religious fanatics also do what they do in order to find favor in the eyes of beautiful partners with similar views. You’ve turned us into animals.

The problem, in my opinion, arose because people started moving away from the king-slave mindset. And they realized they were being cheated. And that their sexual drive is exactly the same as the king’s sexual drive, and that they too deserve a wife.
It’s simply a result of human beings discovering that it’s unfair. Unfair that someone who wasn’t born rich, or handsome, or with high status, won’t merit a wife.
But that created frustration. Frustration among women. They were restricted. Suddenly they have no choice and have to marry men they don’t want.
In short: a mess.

A. In nature there are no rights, and therefore the state can certainly regulate the affairs of society even if that harms certain individuals. That does not mean I accept every foolish custom; I am not a conservative, and for me too a custom with no rationale is a custom of Sodom. But if a custom has a rationale, I do not rush to abolish it. In this context autonomy is a value, but it can only be realized on the basis of basic decency in a proper and orderly state.

B. Greater and better people than me have already pointed out the connection between polygamy and corruption and decay in the East. Parenthetically, in my view part of the corruption and decay of our society stems from the spread of permissive polygamy in our society. And it is no accident that there is a connection between the permissive left and polygamous Muslims. In light of that, monogamy is definitely a custom that has a rationale. In addition, monogamy also works in favor of women when it leads to social improvement and progress.

C. I did not argue that sexual blurring and sexual confusion are a moral problem. I argued that these phenomena, especially among young people, are the price paid for a society that is mixed at such an extreme level that we are not prepared for it. The crazy intrasexual competition in a mixed society over attracting the attention of the other sex causes anyone who doesn’t fit into the right masculinity/femininity slot to suffer. And in that situation, someone who takes longer to settle into mature patterns, someone whose body structure is not distinctly feminine or not distinctly masculine, finds himself or herself constantly humiliated. And in that place, the pattern of thought that leads to sexual blurring and sexual confusion finds fertile ground. If the sexes were separated at that stage, those same young men and women would get their chance to find a more accepted place and not fall into confusions and doubts.
It is common among liberal religious people to lash out at religious people for advocating separation between the sexes. Not many bother to think about the price paid for a mixed society in terms of the individuals within it.

D. I did not argue that we are only animals. At the same time, it is hard to deny our animal side. We eat and drink, excrete waste, mate, and even die like animals. Since empirical studies have pointed to the effect a mixed society has on the behavior of individuals, this is beyond doubt. Provocative behavior and undermining society’s institutions can come from a genuine place, or from an attempt to take up a position that will socially mark the person taking it as a desirable male. I understand that this sounds shallow, but I am convinced that if academia were not mixed, the amount of provocations it produces would decrease. Haredi and religious rabbis generally avoid mixed company, and therefore the temptation is smaller, although it exists there too, and the Talmud already expounds that the Jewish people were jealous of Moses our teacher regarding their wives. In short, I did not claim that this is the only motive, but in my opinion it definitely exists.

And in the context of sexual blurring, is the Rabbi in favor of castrating children (and castration in general), what is called sex reassignment surgery?

https://www.mako.co.il/pride-pride-events/2020/Article-e28b5417217c271027.htm

The way the question is presented reminds me of demanding that I prove that my sister is not engaged in the world’s oldest profession.
I oppose castration (halakhically, not necessarily morally), but I am not necessarily opposed to sex reassignment surgery. In my view it is no different from any other surgery or treatment. When it comes to children, one must of course make sure the decision is made with full understanding (preferably not until they are older). But when מדובר an adult, I don’t see a problem with it.
First, I do not know whether surgery can be done in such a way as to attain the fertility of the other sex (if someone transitioned to female, can that person give birth? And vice versa). But even if we assume not, when it comes as a side effect, there is not necessarily any prohibition here. A person undergoes surgery in order to make life easier, and as a side effect loses the ability to reproduce. Who says such a thing is forbidden? That takes us into the discussion of an inevitable result that one does not want, or of a case where it is impossible to avoid and one has no intention toward it, etc.
And from another angle: suppose having children causes me psychological harm. Am I obligated to enter into that in any case? I really don’t think so.