1) Legalizing prostitution will cut down on sex trafficking.
True, it won't stop the complete monsters with sick tastes but it will help with the casual johns who just want a good time for a night. The reason why teen prostitution and sex slavery is so prevalent is because those illegal suppliers focus on teenagers to cater to both.
Take the Lawrence Taylor case, for example. He went riding around to procure the services of a prostitute for the evening. He hired one he thought was over 18. The prostitute was actually 16. He was charged for having sexual misconduct with a girl under the age of 17. He plead guilty to patronizing a prostitute and sexual misconduct.
Now L.T. was looking for an underaged prostitute. Rather, he was looking for a prostitute, and because it's illegal and unregulated, he got caught up with an underage prostitute.
By legalizing prostitution, underage prostitution and underaged sex trafficking will diminish.
2) It's safer for the prostitutes
Because it's legal and rules of its operations can be done in the open, it allows for more safety measures to be followed that will protect the prostitutes. For instance, laws could demand that prostitution is allowed only in brothels.
This protects prostitutes, who risk their lives every time they perform their work. They have to go someone hidden and out of the way of law enforcement, whose jobs it is to protect the well-being of people. This makes prostitutes prime targets for assaults and murder.
Legalizing prostitution will allow prostitutes to operate in the open and with security to protect themselves.
3) It's safer for the customer
It's safer for the customer because prostitutes can perform other crimes, such as robbery, on potential customers. Now this may sound funny for male customers of prostitutes. But what about female customers of prostitutes? Women are just as likely to solicit the services of a prostitute, be they male or female, as men. So this reduces the risks to female customers too, along with male customers.
4) It's healthier for the sex industry
By regulating the prostitution industry, steps can be taken to provide safety measures can be taken for the well-being of prostitutes and the customers.
For example, every prostitute would need a license to operate. In order to get that license they'd have to first take an course on sex education. This course will give them detailed information on how to maintain sexual health. They will also have to get tested for STDs on a regular basis.
This is a much better alternative to street prostitutes may be uneducated on safe sex and are prone to drug abuse which vastly increases their chances of catching STDs and other illnesses which may go untreated and therefore further increases the chances of them being spread to others.
So there. At least 4 ways in which the legalization of prostitute have social benefits.