The DMCA covers bypassing technology that prevents the copying of protected works. I don't think it was ever intended to cover bypassing the parts that prevent you from using it to protect your own works from copying.
This has actually been the subject of (depressing) scholarly research.
"Further, we conclude that the exemption proceeding is constructed not to protect noninfringing users, but to limit courts' ability to exonerate them via the traditional defenses to copyright infringement."
