I don't think it's moral in itself, but I think it's even more immoral to allow the exploitation and trafficking of women to take place. But if we accept that prostitution is inevitable, then I think it should be legalised and controlled, mainly to try and remove the criminal element who control many of the prostitutes, and also from a health perspective. It's not an ideal solution, but it might help solve some of the problems which exist today. Women need to be given the opportunity to leave and find an alternative job, and while the industry is controlled by criminals, that's not going to happen.
I also think we need to stop a lot of the social stigma that we place on prostitutes to the extent where we ignore the men who use them, who actually keep the industry going. But that's another issue altogether.