So, what's the difference between the "fat doctor" and Jimmy Swaggart with a prostitute? If a justified ad hominem obtains when the critique and the character failing coincide, then either the fat doctor is being hypocritical for suggesting dieting, or Swaggart's statements about Christian character and morality stand regardless of his own failings. In other words, the doctor's guidance may be good regardless of the doctor not adhering to it, and the same goes for Jimmy. Does that make sense? What am I missing? I'm not seeing the difference between the two.
Don't forget to add in Richard Carrier to your list for good measure...
From just the brief article alone, Yvonne Raley cites Walton as describing some additional evaluative measures we probably could (and maybe should) have in place in the process of determining the level of legitimacy that is expressed in the character of our interlocutors. For the fact that various levels of hypocrisy can come into play, this may very well affect the extent to which we think we are even being offered the so-called "truth."
For instance, I can read something like a Richard Carrier essay, and in the midst of that reading, my mind will currently think of two things: He exaggerates some of the points of 'truth' he makes as he floats along in his descriptive articulations, churning out what I think are acerbic commentaries about the Christian faith. At the same time, I also know from other sources something about his character. So....all the while I can hear and listen to his assertions, some of which may be true to some extent, this means a few things for me, things that I think can be said ABOUT HIM without me committing an ad hominem fallacy: Carrier exaggerates
AND Carrier isn't the most moral guy around; he makes excuses for his behavior rather than facing it and repenting of it,
AND because of these existing complications in his own point of view, these 'things' make it difficult for me to assess his interior motivations which drive his acts of critical assertion against Christianity.
Of course, for the sake of fairness, I'd then take the shoe off and put it on the foot of someone like Jimmy Swaggart and see if it fits. (And by golly, it's a pretty close fit, in my estimation!) And I at times will put the shoe on my own foot---and I've found that my foot undergoes various mutations when doing so. Sometimes it fits; sometimes it doesn't. [In fact, it's
Incredible for me to see what happens when I put the shoe on my own foot ...

]
So, we might surmise that full-bodied hypocrisy is one factor in any interlocution and its presence deserves criticism and might be something that should sway us to 'reconsider' the extent that we're ACTUALLY getting the truth from another individual. It might be that what we're getting is a half-truth when a hypocrite speaks. If so, then we're going to have to more fully engage not just the message offered up to us from another party for our consideration, but the quality of that person's moral life and his or her motivations that drive it all.
Now, what other factors, other than hypocrisy, might come into play in our making personal criticisms of others and our expecting not to be charged with making an ad hominem fallacy? (This is a question for everyone, really.

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Thanks for your well-placed comments, PH!