This very much depends on what part of YouTube you tend to be in. Much like any online massively-used portal, different segments of videos will attract vastly different users and types of comments. There is somewhat of an over-generalization of YouTube comments, where the description of toxic comments seems more accurately applied to truly /viral/ videos: those that have broken beyond normal segment boundaries, and where the 'best' comments are perceived to be those that draw the greatest reaction, as opposed to genuine commentary on the video itself.
I'm surprised they don't just disable comments for viral videos, too.
Now that I think about it, imagine the equivalent of that for other services. For example, imagine if all of Reddit's "default" subreddits (the ones that make up the front page when you're not logged in) had no comments attached to posts. To get comments, you'd have to opt into a community. (Which might very well just be a post-for-post mirror of a "default" community, but with comments enabled.)
