Google's algorithm for determining what is a "valuable" comment to promote on YouTube with its new Google+ integration includes how many replies it generated. This means trolls, who post exclusively for the "glory" of inciting as much rage in the general public as possible get promoted comments for it - exactly what they wanted. This makes the fetid cesspool of YouTube comments an even less desirable place to be, giving it over entirely to the trolls and ensuring that the rest of us never, ever read or bother writing any comments on videos ever again.
If Google wanted to shut down the YouTube comments section without actually taking it away, they couldn't have done a much more effective job than this.
Mokalus of Borg
PS - Then again, I haven't bothered reading YouTube comments in a very long time.
PPS - It was terrible before this. Google+ just made the worst more accessible.