Free Software

Liberty, I was wondering you could help me understand the "Free Software" movement, which is explained at http://emoglen.law.columbia.edu/publications/anarchism.html and other sources.

I understand that they want open source codes. I don't understand the economics about allowing copies and derivative works to be distributed for free.

I'm not interested in critiquing this movement (yet), so much as learning and understanding their point of view.

Since you're the computer programmer / philosopher, I was wondering if you could help me out on this one.