It seems there was an innocence coupled with the idea of the brothel. There is something to that I think. A lot of substance and culture involved, is it right to judge these places as a "social plague"?
We evolved to a people who had, now, to adjudge them as social plagues because we were now making to effort to care what happened to our women. As far as substance, and culture, few of these establishments existed as more than simply a business, a way to make a good buck, for the madames at least. And of innocence, there was none.