1. Prostitution industries are non-harmful
2. Prostitution industries are harmful to women no matter what the social context and always will be
3. The industies are harmful to women as a class today and throughout history, under the system called "gender", where men assign to women the role of stores of resources to extract, which has existed as long as civilizations have.
Many people are, genuinely or otherwise, treating the original commentor like he was asserting #2, when he was asserting some variant of #3, which does not logically have #2 built-in. You don't have to agree with the latter part of #3 to understand that it is not the same as #2, and we can start talking about 1 vs 3 without having to resolve 2 immediately.
I mean, we already know this, don't we? We can talk about how to deal with racist institutions without always falling back into questions of "what is race? in a post-racism world, would races exist?" Maybe the analogy isn't perfect...
I think it does matter - in fact this seems to be exactly the pain-point in this whole thread, that everyone differs on that particular point. If it isn't inherently harmful (and again, I haven't thought about it enough to decide), then your line of argument seems to conflate feminist causes with sex workers', and we'd be trampling over a non-harmful industry just to further the cause of feminism [^].
On the other hand, if it is inherently harmful, there's no need to entangle the two either, and we should legislate against it regardless of whether it damages women as a class or not.
Thanks for all the links.
[^] edit: which may be a legitimate reason, of course. But it would avoid most of the discussion in this subthread.