Seriously, we're talking of a tool whose purpose is to download publicly available videos. What's the big deal? It's not even used for music piracy, for God's sake. I've never seen anyone download their favourite album from YouTube videos and use ffmpeg to extract the mp3s. Most of the folks just use Spotify.
So what's the big deal? That if we use youtube-dl then we don't see ads and we don't get tracked? Oohh, actually that's the whole fcking point, you know? youtube-dl pisses lots of people in the majors not because it's used to illegally download musical content (I'm pretty sure that's only an insignificant fraction of its usage), but because it hurts their "new" way of doing revenue: ads, tracking, and more ads.
And you know what? I'm more than happy to hurt such a shtty way of doing revenue!