I think it's safe to say that the Web 2.0 user-generated content sites were not envisioned (by either side) when the DMCA was drafted. These sites have made it so easy to share content and their business model does nothing to discourage infringement (compared to traditional Web hosting); these factors have shifted the balance so that infringement is much easier than enforcement. I don't know how to fix that, especially since there's a powerful status quo bias now that Web 2.0 has existed for so long.