I believe music file sharing promotes music sales. The bands I've worked with over the last three years also believe making their music available over the internet will promote sales of both CDs and tickets.
This is a link to a Wired article, dated April 2000, that states sales rose despite digital piracy.
This is a link to a Salon article, dated July 2001, that states CD sales declined since Napster's file sharing was limited by the courts.
During the Napster proceedings many artisit supported the file sharing software and came out against the recodring companies.
Done Henley came out against the industry claims of copyright infringement on a work for hire endeavor, reported in November 2001 in this CNET article. And there's an impressive list of Napster supporters available on the software maker's site featuring quotes by Chuck D, Dave Matthews and Madonna
here.
Music file sharing can, and does, promote a stronger music industry.