An honest reply could be, say, "it's true that, if I use a prostitute, there is no way of knowing whether she is consenting or if she is financially coerced and

An honest reply could be, say, "it's true that, if I use a prostitute, there is no way of knowing whether she is consenting or if she is financially coerced and it is therefore forced, but is the same not true of clothes? How do I know the shirt I'm wearing didn't have slave labor involved in its creation?" To which one may respond by, for example, pointing out that clothes are general necessary for human life, while having sex is completely optional. But such acknowledgements (that use of prostitutes without the possibility of rape is impossible, that sex is optional) would betray the sex-positivity line and the rewards that come with sticking to it.