The benefits of legalization for sex workers is substantial. They can operate like a real business and do not have to work in the shadows. They can get insurance, rent a business premises, hire security instead of being dependent on a pimp, have access to banking and payment systems (credit cards, etc.) instead of having to carry cash and having to keep their money out of the banking system to steer clear of the IRS. Regulations can reduce STD by requiring testing for sex workers and clients, as well as condom use.
But the big problem is that the capitalists will get involved and invariably exploit the sex workers for bigger profits for investors. Higher demand will be met with more supply, which will then create more price competition. The main benefit of sex work for women is that they can make a lot of money while working part time hours. That allows sex workers to go to school, care for family, etc.
And that gets to the problem of exploitation in general. The percentage of sex workers who were sexually abused as children or young adults is very high. And the number of sex workers who are also addicts is also a big issue. If there are women who are not addicts or suffering from the effects of sexual abuse who are sex workers, the odds are then pretty good that they are sex workers because of the money and would be happy to do something else if it paid as well as sex work. That leads to the big point for me in the legalization debate. Before we legalize sex work, we should make sure that women have access to jobs that pay well and allow them to be parents, attend school, etc. If women made $120k a year as an elementary school teacher, $80k as a home health worker, etc., I think you would not see very many women going into sex work.