"Freedom" to sell your body to anyone willing to pay in order to be able to live is no freedom at all, no matter if it's done legally with guidelines or illegally without them. This is also true for all other forms of work, but prostitution is one of the highest forms of worker exploitation and also a continuation of the oppression of women in particular.

A society free from exploitation and classes has no real incentive to exploit others for sex, maybe in certain cases it can be done in a way that is not oppressive, but under a system based on exploitation, prostitution will always be oppression. Perhaps in a socialist country people could offer sex work as a service by their own free will, but they will not have the looming threat of homelessness and poverty if they no longer want to do it.

As long as we're in capitalism though, all prostitution is exploitation and oppression. It's debatable whether it should be fully legalized in order to protect worker rights, as much protection as capitalists are willing to offer anyway. One thing is for certain though, hang every single pimp by their dicks