I think the point is that you can strongly disagree with a statement without painting its author as incompetent. Regardless of whether that was the intent, that's certainly how it reads.

Going one step further, you can strongly disagree with a statement without attaching a value judgement to the other person's argument.

In spirit, this rule should hold even if you aren't attacking the author directly but are disparaging the value of their perspective.

That is simply unnecessary and you can just refute the point directly.

I don't see much daylight between "utter nonsense" and "that is idiotic".

I think you are being too harsh on parent.

How is that worse than people literally calling each other's comments bullshit on HN?

Examples: https://news.ycombinator.com/item?id=6805295 https://news.ycombinator.com/item?id=5111959 https://news.ycombinator.com/item?id=6410617 .. and many more

It isn't worse - it's the same thing.