A compelling argument on Question Copyright is that a Free License actually preserves your rights. When working for Atlas Games on Occult Lore, I signed a Right to Work contract -- which means that my Elementalism became the property of Atlas Games. Although I have a great respect for John, I effectively signed my rights over Elementalism to have it published. It was a great idea at the time, however times have changed and I've changed as well.
A free license protects the artist's and author's rights of a project. Many proprietary publishers actually want to buy the exclusive rights to your work. Working for an RPG publisher is no different. Eberron isn't owned by Keith Baker, it's owned by Wizards of the Coast (in some ways, that is bad). So that means that Wizards of the Coast owns all the rights over Eberron. All of them. In some cases, signing away the exclusive rights to your work means receiving a royalty check paying you one red cent for life. This is true in the case of Bob Ostertag who receives one cent royalty checks (note though, I do not know the situation between Keith Baker and Wizards of the Coast -- I'm just using Eberron as an example of what happens when an artist signs his exclusive rights away). Sometimes, though, and I'm not vouching for Keith; an artist wishes he could give a piece away but the publisher won't let him.
Of course using a free license means giving up the ability to restrict other people from copying your work. But it also means that they can't restrict you either. A free license allows you to do what you want with your work, while letting others do the same. It's pretty much a win win situation. I really do believe that the danger to the economy is just an illusion. The actual danger to the public is an artist signing his exclusive rights to his work away in a contract.