I don't think you understand. Yeah, you can sue people for illegally redistributing copyrighted works. However, I am skeptical that you can do the same for people using YouTube-dl to consume copyrighted works. You are downloading the file from someone who has a license to redistribute it, you are just using a CLI utility instead of the page itself. You can't view something without downloading it in some capacity.

I'm not saying there's no possibility this is "illicit," I am saying this is not the same as illegally downloading music off of Kazaa.