It's one interpretation, good for those who accepts the faith tenets of post-structuralism. The other is that it came to exist because of its viability in particular economic conditions.
Also, if acceptance of promiscuity as a social norm really benefits exactly women is a really big question.
"Acceptance of promiscuity" is a bit of a contradiction in terms since "promiscuous" is inherently pejorative. I will say this: "promiscuity" has always been far more socially acceptable for men than it has been for women. Despite "enforced monogamy" prostitution is called the "oldest profession" for a reason and extramarital affairs have been happening for a long, long time. If you want to get nuanced, "enforced monogamy" doesn't really mean "enforced monogamy" because affairs were accepted in certain sociocultral contexts in England and France far before the sexual revolution.
Promiscuity is at first, and foremost was (and still is, in spite of contraception availability) practically more acceptable for men. And monogomy among other things is a constraint on men's behavior - forcing to accept social, and economic responsibilities before fulfilling sexual urges. You are right noting that it rarely worked in any absolute way, but I don't think any law, whether written, or not can be 100% effectively implemented. People steal all the time, but I suppose you wouldn't say it's because related norms are not enforced, right? Monogomy's real application varied over times, cultures, and spaces, but it was certainly enforced by societal pressure, and legally too. Actually, in my father's youth years (and it's not that deep in history) it was hard to have sex before marriage. It was for sure possible, but dangerous for reputation of both participants (probably more damaging for a women, but damaging for both nevertheless). It wasn't US, and "sexual revolution" came to us much later, so that's probably why you may have no living witnesses for it.
Also, prostitution was until quite recent times seen as a moral compromise acceptable only because of long serving soldiers, and sailors. In most societies it wasn't ok for a family man to visit a house of prostitution, and in some cases it was even criminalized.
Philosophy is a deep rabbit hole but cursory philosophy should really be mandatory in secondary education.
I'm not at all affiliated but I found the podcast Philosophise This to be very informative and interesting.
This is arguable with modern society ensuring that support is provided from men. Men are wising up to the long term consequences of pregnancy and relationships with women - see the MGTOW movement.
FWIW, enforced monogamy is harmful to women in some ways (hard to leave a bad relationship), but helpful in others (it's hard to end up a single mom when the norm around unexpected pregnancies is a shotgun wedding).
It'd probably be better if I just ignored the comment. But I think the claim "harms far more people" is absurd if you consider the unequal harms done to women through history, and the fact that they're half the population. The commenter didn't make an effort to engage in good faith discussion with my post so it's unreasonable to apply the same standard to me.
I'm happy to reply to comments like yours though.
The risk of pregnancy is a biological fact with far more severe penalties for women. Enforced monogamy in western societies is part of a broader history of social control that came to exist because it was good at perpetuating itself-- and which also unfairly disadvantaged women.
It's unfortunate that we evolved to be the way we are, but the "instability" we're seeing now is partly a result of fixing much deeper inequalities that've existed for most of human history.
The real source of the present instability is socialized (and partly biological) gender differences in how men and women approach courtship.