No, I will second him on that.
(Usenet is mostly dead and was before my time, so I will not comment on that.)
IRC is usually chill and enjoyable because you have people of the same interests who possess an ounce of technical knowledge in the same space.
Forums usually devolve into repetitive dystopias because of those in power (though there are plenty of antitheses), but the former qualifications usually play in, to a smaller extent, and the semblance of discussion can be maintained.
Imageboards tend to act like IRCs when they are small and you can get the feel for the regulars. However, even when they lose coherency on sites such as 4chan, the sheer transience and abrasiveness (ideally) of the culture is enough to keep the general public and the uninformed from making too much of an impact to drive away the current posters. In this chaos, some semblance of discussion is maintained, though the transience of that discussion is at the flip of a coin, and comment-less content-dumping is a real issue.
Sites like Reddit, ycombinator, etc. force the best and most socially agreeable comments to the top, while leaving those of less universally agreeable nature or singularity to be unseen. Its the Republic of comments, where people represent their opinions by upvoting others. You get insightful information (ideally), but at the cost of any real discussion. Its a pretty fair method for filtering through the content of the web for content aggregation, assuming you trust the tastes of the general population.
Facebook is communication between known friends with your entire social circle peeping at the edge. It is no better than talking in a real social setting except for convenience and content aggregation.
Anyway, Youtube comments somewhat preserve the anonymity of Imageboard, but with all the access of shitbookand none of the content aggregation (the content is literally handed to you, a few scrolls above). Therefore, the only people who post (outside of niche things like YTPMVs, MADS, and other small channels where a content system is actually a nice, parse-able addon), are people who feel the comments to be their soapbox to the world, their 95 Theses, without any of the repercussions of posting on social media sites like Facebook. And what topics are appropriate for such an atmosphere? Anything and everything which incites controversy, of course! So you have all the lovely banter of a midday news channel debate, without any of the coherence or the trappings of the former (which was not terribly much to begin with). Its shit, which does not even bother to wrap itself up in a veneer of civilized discussion, and which serves little purpose to few people. Its the worst of all the above forms of online communication.