Sex is one of the last places where women have more power than men. I believe that illegalizing prostitution and other forms of sex acts is a way for a male-dominated world to try to, yet again, limit the power women have in society.
A regulated sex marketplace is going to mean women can be much more picky about who they choose to sleep with, and can do so much more safely. They can use their sexual power to make financial gains for themselves. I believe this is empowering towards women, much more so than trying to erradicate all forms of prostitution.
There will still be illegal activity, but legalizing prostitution will decrease the noise on activity that actually IS bad (children in sex work, forced sex work, etc).