It's because HN prides itself on "civility". So you can "innocently", "just to be fair", "playing the devil's advocate", "but what about" say any offensive thing you like, and when someone who's sick of hearing that bullshit uses a naughty word they get downvoted for being "uncivil".

The rest of the internet figured out long ago that such behavior is actually pretty toxic, and is called "sealioning" [0][1]

[0] http://wondermark.com/1k62/

[1] footnotes. It's all civil if you have footnotes.