Surely the only arguments you could offer against legalizing prostitution would be that it encourages physical abuse of women, who are being taken advantage of, and go down the whole human trafficking argument route, but their is an easy and sensible counter to this, which is to say, fine, I totally accept that human trafficking and rape and women being taken advantage of is bad, make them illegal, but the crime is the abuse and rape and kidnapping of the 'prostitutes', not their act of prostitution. It seems to me to be a continuous problem in all law making that government officials invent new laws to try and stop things happening, when the existing laws already cover that. For example, if a large number of murderers happen to also knit in their spare time, it is obviously silly to make knitting illegal, seeing as murder is already illegal. In the same way, the prostitutes are often abused by their pimp or manager or whatever, and so it is the abuse and the maltreatment that is illegal, not the prostitution.