One of the most tedious aspects of online debate is that, as soon as you call someone an idiot, or suggest that their argument is of the kind that would disgrace a below-average chimpanzee, they accuse you of arguing ‘ad-hominem’, which they believe to be a terrible thing.
As the holder of a philosophy degree from a mildly respected institution, I can confirm that this is bollocks.
There is a fallacy in argument called the ‘ad-hominem fallacy‘. It applies to irrelevant personal insults (or compliments) – “yes, Dave Smith is in favour of cutting the speed limit, but he drowns kittens in a sack so we shouldn’t”.
However, this is seldom the way the term is used online: normally, it’s used against two entirely legitimate forms of criticism.
1) If you make a revolting argument and I call it revolting, that’s legitimate comment, not ad-hominem (if you make a revolting argument and I call you fat and ugly, that would have been ad-hominem.)
2) If your background suggests strong and unreasoned partisanship for a particular cause, then it’s more reasonable for me to doubt the factual underpinnings of your case (clearly, not the logic of whether your conclusions flow through your premises) than for an impartial observer.
Since all real-life argument outside of thought experiment relies on accepting some evidence that you’re unable to verify yourself, this means that it’s reasonable to form different opinions on the same argument presented by two different people.
For example, imagine a discussion on lowering the age of consent, as presented by a) a well-respected child psychologist b) a notorious paedophile…