Free access to scriptures religious leaders try to censor
The short answer to that question is to protect marriage.
That answer would soon lead to two other questions.
1. How does prohibition of prostitution protect marriage more than prohibition of other forms of free sex?
2. Why bother protecting marriage? A better question would be, “Why some people bother protecting marriage institution?”
Prohibition of prostitution protects marriage because prostitution directly competes with marriage institution. We all want to have sex. Some want us to have sex within marriage. So those people tend to oppose all sex outside marriage.
Prostitution is special because among all sex outside marriage, prostitution is the one directly competing with marriage the most. That’s because marriage is a form of prostitution.
A kid asks his dad, “Dad, how much does it cost to get married?” Daddy says, “I don’t know son. I am still paying.” That’s what marriage is all about. Men pay for sex.
But of course marriage is not just a regular prostitution. Marriage has other features. Some call it, “sacredness”, “holiness”, “love”, blab la, etc.
In other words, marriage is a regular prostitution plus a bunch of irrational bullshits.
Those bullshits give governments various justifications to interfere in marriage with various restrictive rules, such as prohibition of polygamy to ration females in equal share for every one. Such restrictive rules, cause market distortion.
Now, all market distortion profits somebody right?
Minimum wage, for example, hurt productivity as a whole. However it benefits some workers, causing unemployment for the others, and hurt businessmen. So those some workers that are benefited support minimum wage.
Protection to failing industry benefits the owners of those failing industry while preventing technological progress. Still some people support such protection and subsidy.
So, it’s natural then to expect that someone, somewhere, somehow, want to protect marriage institution so much. That’s because they survive better in the gene pool when such restrictions exist than if they don’t.
Without marriage, some alpha males will mate with all the women. With marriage, the non alpha males get women too. So non alpha males prefer marriage so much.