Music is nice and largely even positive—if repetitive (“anyone here listening to [90s band] in 2020??”)
Facebook insists even more on having "real people" using their real names, often forcing them to vet themselves, yet at times it easily steals the crown in terms of "really bad user interactions" from YouTube comments.
Very likely much more related to the topic under which people are commenting: Non-political feel good fluff does not allow for much friction to be inserted, thus the tone of comments will be much more civilized and friendly.
But anything that goes into controversial, and particularly political, territory is bound to quickly escalate into a complete shit show, on YouTube and Facebook alike.
Which fits neatly into common communication strategies like focusing on similarities rather than on differences.
But the migration of YouTube channels and comments to G+ linked identities was reversed[0], wasn't it? Not to mention that G+ has since been shut down.
Shouldn't that make the abortive effort irrelevant for the quality of YouTube comments today?
[0] https://googleblog.blogspot.com/2015/07/everything-in-its-ri...
A bit offtopic, but when YouTube first added comments, they quickly got into cesspool territory, exactly like you describe. However, these days, I find myself really enjoying YouTube comments quite often. Is this just me? Am I just watching more happy happy joy joy videos these days or did YT comments go from "the internet's awfulest" to "pretty neat" somehow? I feel like it's chock full of witty jokes, positive vibes, light entertainment, and the occasional weirdo just to balance things out.