I agree with you on all that, except that heroin (at least in its pure form, morphine) is deadly. It is not. I know several people who have tried it, and lived, and didn´t even get hooked. And according to Slingblade, the existence of these "responsible users" would mean that heroine (or morphine) would have to be legalised, wouldn´t it?
(now I see that you said "in sufficient dosage". Yes, like anything else, water, salt, sugar, anything. But you don´t mean that do you?)
Of course sex is not inherently dangerous. What I´m saying is that if society allows for the commercialization of sex, perhaps THAT could be dangerous. Or at least not very coherent with the rest of societal laws.
Oh, and what I said about Germany and compelling women to work in brothels not to lose benefits seems to be false. Apparently it was based on an article that speculated on the possibility that it could happen, which snowballed.
http://www.snopes.com/media/notnews/brothel.asp