The problem with the Linux Kernel Developers position on DRM (and this can be seen in Debian-Legal's attitude to the Creative Commons anti-DRM language as well) is that they view DRM as a technology, not as an extension of copyright law. DRM has power only through law: it would not be illegal to remove or reverse-engineer DRM otherwise. But too many hackers idealise DRM systems as code and DRM-laden files as data. They ignore the legal dimension, and this leads to confused reasoning.
To cite the FSD or DFSG freedom to modify code in support of this new excess of copyright law is an example of that confused reasoning. You cannot modify BSD-licensed code to remove the copyright header for example, and you cannot add the string “all rights reserved” to the top of a GPL-2-licensed file, yet despite restricting your freedom in this way neither license breaks the FSD or the DFSG. If the BSD license said “you may not write a script to remove this header”, would that break the DFSG?
DRM is an extension of copyright law that can prevent computer users from exercising their freedoms. Those who support DRM seem to view code, rather than human beings, as the subject of Free Software's freedoms. This is an impoverished understanding of freedom. But if you must write DRM code, the GPL-3 will not prevent you. It just removes the legal privileges that such code would otherwise have to remove users' freedom.
(Originally posted as a comment on Luis Villa’s weblog, reproduced with minor edits for clarity).