"Foul language" is a very rough measure. The parent's thought could have been communicated with less sarcasm ("Sad that ... ?") and bitterness ("doesn't deserve").
Edit: Further, some topics, no matter how carefully broached, are just a bad value proposition. They may have a bad ratio between their intrinsic value (importance, relevance, etc) and how likely they are to spawn a low-quality thread (and how low that quality is likely to be).
Indeed - the implication that a statement merely containing anything factual or backed by evidence makes the whole thing uncriticizable ("but it's true") is maybe the most common fallacy made in defense of provocative statements.
"Delete the whole" is not how threads work on HN. The way that threads work on HN, assuming that they're on topic, is that people should post intellectually curious comments and avoid posting unsubstantive or predictable ones.
Edit: Further, some topics, no matter how carefully broached, are just a bad value proposition. They may have a bad ratio between their intrinsic value (importance, relevance, etc) and how likely they are to spawn a low-quality thread (and how low that quality is likely to be).