A contemporary answer to Bernard Mandeville may be the economist Walter Block. In 1976, Block wrote a book titled "Defending the Undefendable" were he analyzed chapter by chapter different activities generally considered unmoral and justified them using economic reasoning and showing the social benefits that they brought about. In this light, the activities of the pimp, the prostitute, the pusher, the speculator, and many others are described throughout the book.

The PDF version of the book can be found here: http://mises.org/books/defending.pdf