You can read it here. If you haven't already, you really should.
And if you don't buy the Free Meme (pun intended), look around. Music, Opensource software, even the world of street art you can see how giving away your art can create real financial gains.
On 7 February 2007, Sotheby's auction house in London auctioned three Banksy works, reaching the highest ever price for a Banksy work at auction: over £102,000 for his Bombing Middle England. Two of his other graffiti works, Balloon Girl and Bomb Hugger, sold for £37,200 and £31,200 respectively, which were well above their estimated prices. The following day's auction saw a further three Banksy works reach soaring prices. Ballerina With Action Man Parts reached £96,000; Glory sold for £72,000; Untitled (2004) sold for £33,600 - all prices being significantly above estimated values. To coincide with the second day of auctions, Banksy updated his website with a new image of an auction house scene showing people bidding on a picture that said, "I Can't Believe You Morons Actually Buy This Shit."It get's better. Less than a year ago, this work (below) sold for over half a million dollars.
If you create value, even when you're not trying to and you give it away for free, society will find a way to create value around it. Even if, in Banksy's opinion, your a moron for doing so.
On April 27, 2007, a new record high for the sale of Banksy's work was set with the auction of the work 'Space Girl & Bird' fetching £288,000 ($576,000), around 20 times the estimate at Bonhams of London. On 21 May 2007 Banksy gained the award for Art's Greatest living Briton. Banksy, as expected, did not turn up to collect his award, and continued with his notoriously anonymous status.