I would say HN has by far the best signal/noise ratio for comments of any site I read, but even here, the "I'm glad I read that" comments are maybe 10% of what's posted and the "I fear for humanity" is about the same.
YouTube or any local newspaper are the extreme examples, pretty much 100% "I fear for humanity" comments.
Ars Technica and The Verge seem to well above average, but they're 5% good/45% ignorable/50% freaking awful.
Engadget or any Gawker site seem to be about average for the Internet, 1% good/10% ignorable/89% freaking awful.
I guess what I'm saying is, with very very few exceptions, my personal experience on most sites (including small blogs with high quality content) has absolutely been that the comments are not only a distraction but almost always just make me depressed if I bother to read them. If I want to read comments on a particular article, I'd much rather do it on HN or (maybe, sometimes) a good subreddit.
If so, that's still not good...
Yes, the comment systems of major blogs such as Engadget and TechCrunch are filled with filth. (disclosure: I gained my fame/infamy through the TechCrunch comments section). That's when the GIFT and Law of Large Numbers meet, and it isn't pretty.
But high quality content yields high quality content. Articles that are insightful, like analyses that hit the top of HN, don't attract stupidity. Playing curation games with your comments (such as Gawker's "we hide all your comments unless we like you.") alienate your users, and it is somewhat selfish from the author's perspective.
A good compromise is Facebook Comments, which discourages trolls who aren't willing to be anonymous. It doesn't eliminate them, but it's a very strong start, and easy to implement.