I'm not sure it is this. Instead, I think it is that conservatives think that sex work is fundamentally immoral and that therefore it cannot be accepted by society, regardless of any harm or benefit created by this policy. It isn't "hey we believe that sex workers fundamentally cannot be protected from abuse" like something like child labor but is instead "sex work is moral degeneracy and must be stopped."
“Moral degeneracy” is a problem (in their view) because of the associated harms — which we’ve learned over time and encoded into our traditions. That things they call “moral degeneracy” fundamentally are harmful to a healthy society and to the people involved.
That is, they think sex work is harmful to the people who participate and those nearby (eg, children of sex workers).
Morality isn’t merely arbitrary and capricious rules, but an evolved code of conduct which tries to avoid things that are harmful. (Or at least, were — eg, prohibitions on pork.)
> “Moral degeneracy” is a problem (in their view) because of the associated harms
You're assuming the social conservative subscribes to a consequential ethics system. But a social conservative subscribing to deontological ethics is more likely, particularly if they're a religious social conservative.
Well, the modern conservative movement is an alliance of several groups.
Some conservatives get from sex work to prohibition via moral degeneracy - perhaps they'll want strong moral fibre from their politicians and oppose all forms of corruption.
Other conservatives reason via religion - perhaps they'll also oppose teaching evolution, and support 'in god we trust' signs in classrooms.
Still other conservatives don't really care either way about prostitution, but have strong opinions on guns or taxes and kinda tolerate the rest of the conservative platform.
And there are even conservatives who think the state has no business regulating what goes on between consenting adults behind closed doors, and the smaller and less intrusive a state is the better; and they're frankly embarrassed their fellow conservatives are inviting the state into the bedroom.
Not so. Consider gay sex. Conservatives consider this to be "moral degeneracy" and seek to ban things like gay marriage or even gay sex altogether. Occasionally, conservatives will claim this is about protecting gay people from disease but this is obviously a lie because
1. they never exclude gay women
2. they don't actually follow through on other policies to prevent STDs in the gay community and even frequently consider things like HIV to be divine judgement
It becomes clear that the concern about "moral degeneracy" is not at all related to a desire to keep gay people from experiencing harm.
Similarly, the concern about "moral degeneracy" related to sex work is not at all related to a desire to keep sex workers from experiencing harm. Instead it is about "protecting" society from what they perceive to be evil harlots.
