I’ve also been around for years, but I don’t see it as a recent phenomenon. I’ve noticed that usually most top comments (for most topics) contain contra-arguments, or critical comments of any sort against the article. Sometimes it’s useful to learn about other perspectives, but often it feels forced or just plain negative/ego inspired. I could go back years and check old posts and notice that same trend. One famous example is the Dropbox post.

General bitter people stuck in the 9 to 5 grind

The vast majority of people in here are posers, i.e. not hackers in the old-school computer wiz sense, nor hackers in the Paul Graham sense.

HN has gone mainstream a decade ago. Now we've got the same audience of Ars Technica and r/technology.

New users are more likely to be positive, actually. HN has always been more negative, it even has the infamous Dropbox comment by BrandonM.