It's not about condemning bias, qualifying the rightness/wrongness of comment or "caring about his day job" but about arguments in good faith. Not declaring affiliations or potential conflicts of interests makes people ascribe negative intentions or deceptive motives to you (even when not necessarily the case) if they discover it after the fact.

It doesn't have to be in more formal settings such as in publications by journalists - I also see disclaimers stated by others in HN comments often.

Arguments in good faith do not require source disclaimers. That's the very definition of good faith.

"potential conflicts of interests makes people ascribe negative intentions or deceptive motives to you (even when not necessarily the case) if they discover it after the fact."

This is, in my experience, nonsense. The only thing disclaimers add to a good faith discussion is the ability of people to do exactly what you claim they'll do "after the fact", during the discussion. Please stare at any comment with a disclaimer from a group people don't like (uber, for example), and count how many comments are about where they work instead of their argument.

IE They are upset they turned out to agree with someone that belongs to some group they don't like, or whatever.

It is also against the very definition of good faith you describe to do that kind of thing "after the fact", regardless of who you are. The fact that you believe disclaimers are necessary to a good faith discussion means you aren't actually having discussions in good faith.

Is source evaluation not part of critical thinking these days?

It certainly was in all my research courses when I was in school.

Or do you just mean I should have to click to do the source evaluation?

For unverifiable claims, perhaps, but it's usually far better to simply ignore all unverifiable claims in the first place. It's not useful in debate, either, better to simply to stick to debating what facts (if any) formed an opinion, as at least those can be researched.