The feeling that it is immoral comes from the fact that with us the word morality means not only harming other people—that is, ethics—but also a life of abandon, meaning a life of gluttony and drunkenness and so on, a life of addiction to desires and chasing the satisfaction of impulses. (In fact, in the U.S. too they call this morality. For example, police departments there have a vice squad that enforces prostitution laws.) There is also a feeling that a life of abandon (in Michi’s language, aesthetic morality) somehow also leads to crime and violations of ordinary ethical morality. That is why in the overwhelming majority of Western countries prostitution is illegal to sell (except for four places: Germany, Australia, Nevada in the U.S. because of Las Vegas, and one more that I don’t remember). The sale and use of hard drugs, and even light drugs, are also forbidden in almost all of them. And indeed this was also the main dispute between Sparta, which educated its children strictly for military lives of modesty, and Athens, which educated them for a hedonistic life of philosophers and produced weak-spirited people with no backbone. And in fact Sparta led the Greek cities that managed to stand against the Persian conquest.

The issue of harm to the family is only part of something bigger: that the wholeness of human society, with its human achievements, which enforces and encourages ethical morality (without which it cannot exist; without it there is only a jungle, with no technology, spiritual life, etc.), depends on a life of order, governance, and meaning, and striving toward a goal—not just a life of being swept after impulses, emotions, and desires. A life that contains the realization of wants, not the chasing of momentary pleasures. And still, I really don’t have a full explanation of why abolishing aesthetic morality would lead to abolishing ethical morality, but there is a very strong feeling that this is true (beyond the trivial explanation that a person who is used to acting to satisfy his impulses will have trouble stopping them when it comes to harming others, especially when that interferes with satisfying an impulse of the usual kind that he spends the rest of his time pursuing. After all, people steal because they need the money to obtain fulfillment of their ordinary desires, which in themselves do not contradict ethical morality. It’s not that people have a special desire specifically for the act of theft itself.)

And in fact, to this day I haven’t seen any liberal (even among those who support legalizing prostitution and banning drug use) who is willing to abolish the law against people having sex in the middle of the street, or even walking naked in the street. Even though in principle there is nothing immoral about it. After all, people also kiss in the middle of the street.

Enforcement against prostitution is because of the damage it causes and because of the perception that it is not done out of truly free will. Those are moral problems in the usual sense.
As for relations in the street, that is a matter of disgust, not morality.

The enforcement against prostitution was always only because of the harms it caused, but the harms it caused (that is, the crime around it) stemmed from the character of the profession as something disreputable (immoral). That is why there were claims that it should be institutionalized. That was the case until the middle of the previous decade, when the progressive nonsense began, about banning prostitution because it is not really done out of free will (a claim like that could be true regarding every person’s choice of evil in the world throughout history…). And in super-progressive Germany, prostitution is still legal to this day. In the end, the progressives not only remove responsibility from the women, but even transfer the responsibility for prostitution—quite brazenly—to the men who consume from the women who provide it, because of their view that women as a social class deserve privileges because of their victimhood and weakness. But the men consuming it also had victimized life circumstances that led them to consume prostitution instead of obtaining sexual relations from girlfriends or women… It’s more or less like transferring responsibility for selling drugs from the dealers to the users who buy from them…

In any case, a true liberal should not prohibit by law activities that are not immoral just because of the harms they cause. By the same token you could also forbid eating junk food, or football games and other things that lead to gambling that leads to crime, or forbid drinking alcohol, etc. Apparently prostitution was also seen as something bad in itself (as with gambling and drugs), and the harm caused by it was the final hammer blow in prohibiting it—as a sign and not only as a cause, or “let it combine.” And even in countries where prostitution is institutionalized, there are still problems of trafficking in women (from underdeveloped countries) for prostitution, and that was apparently created because of the lust-driven nature surrounding it.

And besides, for a true liberal, since disgust is a matter of taste and not morality, it cannot be that a matter of taste should limit what people can do in the public sphere, can it?

If we isolate the discussion and talk only about the prohibition of a married woman as a forbidden sexual relation, then yes, in my opinion it is immoral even without the Torah, and here again the destruction of the family structure definitely comes in.