How to Disagree 18 years ago
Curiously, I've heard DH1 (ad hominem) invoked in Computer Science circles. More than once, I've heard someone say that it's likely that P != NP, because lots of Very Smart People who've Worked Very Hard on the problem, and haven't able to collapse them. Of course, this isn't really a use of ad hominem argument in disagreement, it's a use in support of a claim.