I think the idea is that by hurting sales of DRM-ed books relative to DRM-free books, and by increasing the piracy problem only for DRM-ed books, you make it mo

I think the idea is that by hurting sales of DRM-ed books relative to DRM-free books, and by increasing the piracy problem only for DRM-ed books, you make it more attractive for publishers to sell DRM-free books, and for authors to apply pressure to their publishers in that direction. Of course, you have to put your money where your mouth is by actually buying books from DRM-free publishers (like Baen and Tor).