For me -- for pretty much every writer -- the big problem isn't piracy, it's obscurity (thanks to Tim O'Reilly for this great aphorism). Of all the people who failed to buy this book today, the majority did so because they never heard of it, not because someone gave them a free copy. Mega-hit best-sellers in science fiction sell half a million copies -- in a world where 175,000 attend the San Diego Comic Con alone, you've got to figure that most of the people who "like science fiction" (and related geeky stuff like comics, games, Linux, and so on) just don't really buy books. I'm more interested in getting more of that wider audience into the tent than making sure that everyone who's in the tent bought a ticket to be there.
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So ebooks sell print books. Every writer I've heard of who's tried giving away ebooks to promote paper books has come back to do it again. That's the commercial case for doing free ebooks.
Now, onto the artistic case. It's the twenty-first century. Copying stuff is never, ever going to get any harder than it is today (or if it does, it'll be because civilization has collapsed, at which point we'll have other problems). Hard drives aren't going to get bulkier, more expensive, or less capacious. Networks won't get slower or harder to access. If you're not making art with the intention of having it copied, you're not really making art for the twenty-first century. There's something charming about making work you don't want to be copied, in the same way that it's nice to go to a Pioneer Village and see the olde-timey blacksmith shoeing a horse at his traditional forge. But it's hardly, you know, contemporary. I'm a science fiction writer. It's my job to write about the future (on a good day) or at least the present. Art that's not supposed to be copied is from the past.
Finally, let's look at the moral case. Copying stuff is natural. It's how we learn (copying our parents and the people around us). My first story, written when I was six, was an excited re-telling of Star Wars, which I'd just seen in the theater. Now that the Internet -- the world's most efficient copying machine -- is pretty much everywhere, our copying instinct is just going to play out more and more. There's no way I can stop my readers, and if I tried, I'd be a hypocrite: when I was 17, I was making mix-tapes, photocopying stories, and generally copying in every way I could imagine. If the Internet had been around then, I'd have been using it to copy as much as I possibly could.
There's no way to stop it, and the people who try end up doing more harm than piracy ever did. The record industry's ridiculous holy war against file-sharers (more than 20,000 music fans sued and counting!) exemplifies the absurdity of trying to get the food-coloring out of the swimming pool. If the choice is between allowing copying or being a frothing bully lashing out at anything he can reach, I choose the former.