Ad hominem is considered bad form. But in this age of disinformation the postmodernists warned us about, analysis of information sources shows itself to be a crucial element of critical thinking, whether that source is your grandma or the propaganda outlet of a cult. I’ve been accused of “attacking” people online after what I see as my efforts to criticize their arguments in a constructive way. And we all run the risk of feeling defensive or bullied when our positions are challenged. The answer, for me, is to adopt a critical identity. And in that adoption, a taxonomy of attacks falls out. Making fun of someone’s haircut is fundamentally distinct from identifying a common trope in their steelmen attempts. I assert most people are sensitive to that difference, if they can step outside their self. Questioning a source’s assumptions, incentives, motive, and rhetorical history is a perfectly legitimate way to criticize an argument from that source. How one gets to some conclusion is as important as the soundness of the conclusion itself. I.e. even in reasoning, a mechanism is necessary.
An enlightening example of the class of criticism in which ad hominem sits starts with Robin Hanson’s Why Abstaining Helps, wherein Hanson makes the argument that we (all) ought to abstain from voting if we judge ourselves too ignorant to do so. I like the counter to Hanson from Dunning-Kruger. If you’re competent to vote, you’ll most likely over-estimate your peers’ competence. And if you’re incompetent to vote, you’ll most likely over-estimate your competence to vote. So Hanson’s argument is at best a wash. At worst, only incompetent people will vote. That’s a relatively layered criticism of Hanson's free-market-like fluid probabilities conception. But this tweet takes it a step further into the context of voting:
@falseworkidol: to me the flaw of this model is that it misunderstands the purpose of voting it's not simply about choosing policies to maximize some objective function, voting is the way we specify the objective function
A vote isn't really a statement of one's competence in determining which candidate will produce the most utility for oneself, the world, nation, whatever ... a typical "rationalist" arrogance. It's a marketing reaction. We're the focus group and we've just been presented with the candidates’ pitches. Our vote is more of a "liked it" or "hated it" response, our constant reminder that the world is impredicative, circularly defined in terms of universal quantifiers.
I used to scoff at those who thought of political campaigns as being about the character of the politician. And would feel disgust at ad hominem attack ads. But I now (think I) understand it. Assessing someone's character and credibility is as much about their assumptions, motivations, incentives, and rhetorical track record as it is about particular artifacts they extrude onto the living room rug. Predicting what a candidate will do once in office is largely irrelevant in a representative democracy. What we're voting on is our assessment of their character, importantly including their reasoning mechanism(s). If you're ignoring that character in your assessment, you are not a critical thinker.