Here are two opposing viewpoints on the proposal to prosecute men for buying sex. Julie Bindel is in favour of it. She thinks that prostitution infringes human rights, 'that women's bodies are not commodities to be bought and sold'. Chris Dillow, on the other hand, calculates the market effects of criminalizing men who pay for the services of prostitutes and argues that it would be the women, the prostitutes, who would suffer from them.
I don't see how either of the two views can be upheld without modification. Chris's argument depends - I think - on an assumption that the market for sex is a free or 'normal' market. But because of trafficking and enslavement, or near-enslavement, it isn't. Legal intervention to punish and stop the coercion of women into selling sex, or into selling it on terms unacceptable to them, is certainly justified. That coercion does indeed infringe the rights of the women who are coerced.
But when Julie Bindel says that women's bodies aren't saleable commodities, she's also wrong. As things stand - i.e. given the moral and legal rules we all live under - women, just like men, are free to sell their bodies as also their minds, and they do so all the time on terms agreed by contract and constrained by law. Otherwise there would be no such thing as a paid employee. So what Julie really means is that, though women are free to sell their bodies and capacities, men shouldn't be free to buy the use of these for certain specific purposes, namely sexual purposes. And this I'm not sure about either. Where it's a genuinely free act on both sides, an argument is needed as to why that free act between consenting adults shouldn't be treated like most other free acts. That many women are driven towards the choice by economic necessity or difficulty doesn't seem to suffice as a reason, since many people, of both sexes, are driven by the same pressure into forms of work they wouldn't otherwise choose.
So criminalizing the buying of sex in general seems to me to need further argumentative support than Julie Bindel gives it. But I can't see what the argument would be against criminalizing the buying of sex from women who are trafficked, enslaved, or coerced in some other way. Why can't this be made a strict liability offence, so that not only the traffickers and pimps but also the men buying sex from coerced women can be prosecuted?