Many times when I collapse a thread it will do so weirdly and a few comments will still be left visible. Many times I'll also have a single comment duplicated two or three times.
And that also just because being skeptical of every piece of unsourced information isn't too great when having personal conversations. You don't have to believe every single rumor, but making people prove everything they tell you, that's just not very sociable.
When you look at controversial topics with these two companies in them, you often see a whole load of negative comments and then one or two chains of comments that defend them, declare people being negative about it as being unreasonable and you generally have multiple accounts responding to each other, agreeing that this really isn't too bad. And of course, these comment chains have been voted to the top.
The last part doesn't have to be a result of astroturfing, HN's voting system encourages controversial comments, as more people are able to upvote than downvote comments, but yeah, that doesn't exactly make the platform as a whole a better place.
None of the apps I've seen so far allow me to be logged in (and some I wouldn't trust), so what's the point?