I think you are misunderstanding the legal argument. The DMCA Section 1201 specifically prohibits (among other things) technology that "is marketed ... for use in circumventing a technological measure that effectively controls access to a work protected under this title." The example in the README is evidence of this.
The argument is that youtube-dl is primarily used for breaking DRM not just that it could be used for doing so.
The argument is that youtube-dl is primarily used for breaking DRM not just that it could be used for doing so.