I think what this supposed DMCA is best compared to is making cameras illegal because people take photos and record videos of copyrighted material.
The key difference is in what the real world contains, versus the virtual world — the virtual world is so dominated by intellectual property that it is almost hard to argue that youtube-dl isn’t meant to copy IP by the fact that almost everything on Youtube is copyrighted.
The desire for a library style free archive of important videos, I think, is just, but youtube-dl is not a that. I’m not sure what it is, it seems to me unquestionable that it should be legal, though.