It makes sense as a general behavior since it suppresses flamewars by hiding the original bad post that kicked them off along with the replies (that are likely

It makes sense as a general behavior since it suppresses flamewars by hiding the original bad post that kicked them off along with the replies (that are likely flames). The downside is that when HN posters perform well, they're responding to bad posts with good posts, and the good posts get suppressed. The alternative (sparing rampant flamewars to rescue the occasional good-reply-to-a-bad-post) would probably add fuel to flamewars.