I believe parent's thinking is that a total identity chain comprises all human-influencing bits of identity. Most of these social engineering attacks fuzz boundaries in human-arbitrated authentication systems. And I wouldn't categorically rule out any portion of my identity as never being useful to an attacker.
You're right that not every website is critically important, but that also wasn't my point. My real point is that it is important to treat every website as though it were, because having that decision making ability is dangerous.
I think we mostly agree here though :).
Yet with access to your HN account, a malicious person could damage your reputation and career, and I can imagine different kinds of social engineering that makes "weak link" seem plausible.
I get what you're saying here, but this is patently false. My HN account is not a weak link in my "total identity chain" in any way that matters.
Yes, obviously defaulting to strong passwords everywhere is a better default because you can make mistakes when judging how important a specific site is, but that doesn't mean that every site is critical.