It hurt the fragile person, yes, but let's think of the average person. Calling someone's idea stupid will reasonably insult the average person and make them think you're a cock, unless you know them well enough (in which case all bets are off). I am by no means advocating catering to the lowest common denominator, I'm simply opposed to throwing out all social conventions that have basically been with us for as long as verbal communication has existed because it's "efficient" (no proof either that it's actually efficient). At that rate the OP is simply asking us to stop being humans. It's just nonsense.

> It's just nonsense.

Ah, I see what you did there.

How different is this from “it’s stupid”? Or is there an approved list of ideas one may call nonsense, stupid, or braindead?

Well, if I were to come across someone IRL who argued that we didn't need to be nice to people and observe basic mores that have most likely existed for at least as long as humans have existed, I'd call it nonsense there too, but that's never happened. There's something about the internet that brings out the ridiculously hot takes. It's orders of magnitude more nonsensical (and harmful) than any single bad idea I've ever come across in my time in academia.