First, see this earlier blog entry:
https://dalehusband.wordpress.com/2010/05/15/phony-feminism-takes-a-beating-on-youtube/
It has occurred to me that if acts of prostitution were legalized for both genders and all sexual orientations, then men and women who are otherwise unemployed could offer their bodies to the sexual services of others who are employed and have plenty of money, get paid for it, and thus never need to engage in harmful and even violent activities, such as bank robbing, and they would not have to go on welfare either. Eventually, the unemployed could find jobs and not need to sell their bodies anymore, though they may still choose to do so.
And it need not involve strangers either. Male and female friends and neighbors could engage in sex with each other in exchange for money, as a means of mutual support. I know if I were out of work and a woman offered me money for sex so I could pay my monthly bills, I wouldn’t hesitate to accept the offer, provided I thought she was trustworthy.
It is exactly because prostitution is illegal in most places that so much abuse is associated with it. Legalizing it would result in a less violent and more generous and tolerant society.
Dale Husband's Intellectual Rants 
I’m not sure if the question is so much “What if prostitution were legalized everywhere?” but rather “When will prostitution become legalized everywhere?”
If by ‘everywhere’ you mean the ‘entire world’ then well, it’s going to be a while before we have a (recognized) world governing system that could put something like universally-legal prostitution in place.
If the question becomes “How do we legalize prostitution and therefore get it regulated?” I’m afraid again it is going to take a lot of effort and a lot of time. I certainly have no easy answers.
We are in essence trying to convince large groups of people to change their worldviews, and then also trying to stop them from putting their own personal convictions on other people. Have we ever stopped humans from doing this to one another?