Both 'opinions' or 'facts' can easily be flamewar tangents - the form and context count for a lot. There's lots of moderator commentary on this.

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.

Thanks, by the way.