Just because the RIAA cries foul doesn't mean there is actually anything wrong here. Piracy is illegal, but youtube-dl is not a piracy tool, just like VHS recorders were not piracy tools. Making personal copies of videos is absolutely legal, and seems to be the prominent way to use youtube-dl (Why else would you use it? The content is already available for free on youtube itself!).
So what you should call youtube-dl is "Something the RIAA doesn't like", basically.