It simply asserts that in SOME cases, presumably if the subject at hand is specifically about a person's history and or personal choices, data relevant to such an inquiry CANNOT be considered off-limits.
It explains that an ad hominem isn't fallacious if the position the other has implicates their character/ motivations etc.
It's not about Positive or Negative or such value statements, it's about Correct or Incorrect reasoning, True or False argumentation.
You shouldn't believe someone just because they're a doctor.
You shouldn't disbelieve someone just because they're a commie.
I agree, claims should be examined by themselves but if the creed of the Doctor is to always obfuscate or lie/deceive then it would be difficult not to believe them, the same creed-o would dismiss the commie if that were the case.
Well that's encouraging.
The only "problem" being that you can never know "their character" or "motivations" etc, due to your EPISTEMOLOGICAL LIMITS.
And even the most morally repulsive, malevolent person can still make a perfectly valid logically sound statement.
Their moral repulsiveness and malevolence do not magically invalidate their logic.
I admire your faith in sample-bias.
Please teach me to "Judge Correctly" without logic.