I think you just described most of the reason I like it. Plain text sites tend to scale text, allow pinch to zoom, and are just generally faster.
Post deletion we've seen used for manipulation on other sites, it's a sticky topic. HN seems to want you to stand by your word, so it makes sense here.
That’s a terrible justification, and I would question if it’s even true. Is there anything to support that conclusion or is it just a guess you’ve made?
Because I don’t buy it. There is no time limit for discussions. One can take as much time as they like to enter text on their phone. Also if they’re motivated by the discussion they may take the time and make the effort to write thoughtful replies.
Finally, there’s no reason that users visiting on desktop computers won’t make equally shallow remarks. Shallow online discussions have existed long before smartphones existed.
I believe that's the HN application itself, not a WAF in front of it.