Ad Hominem Arguments and a “Hermeneutics of Suspicion”

In the comments section of another post on this blog, 1 commenter (X) refused to get books on logic recommended by another commenter(Y) because X said Y had previously proven untrustworthy in book recommendations and because Y thought a 3rd individual (Z) was a major religious and political authority, but X distrusted Z enormously.  Y accused X of making the logical fallacy called an Ad Hominem  argument–an attack against the person’s character rather than against said person’s arguments.  Y is right about Ad Hominem arguments: Logicians consider it a major logical fallacy.  Person 1 says that something (e.g., a tax to improve public libraries) is a good thing and should be supported. If Person 2 replies that one should oppose the tax not because of sound reasons (e.g., it will cost too much; it’s the wrong kind of tax; the project is unworthy; the project can be funded in better ways–all logical lines of argument if true) but because Person 1 is (supposedly) a scoundrel who cheats at cards, that’s an ad hominem and does not advance a debate.

But are there limits to the strictures of the ad hominem rule?  What if someone HAS proved to be unreliable on something before or does have a bad character. Don’t we all listen to a person whom we distrust with more suspicion than we otherwise would?  Outside of formal debate, we do this all the time.  Sometimes it is clearly unjustified–and may even be sheer prejudice.  But at other times, such suspicion is surely justified.  If politician P introduces legislation L that financially benefits one of P’s major financial contributors (FC), L may still be a good bill that deserves to become law. But if we the voters (V) find out about FC’s contributions and the way they benefit from L, V will be displeased. V will suspect that L is some kind of kickback for FC’s contributions. At the very least, V will want to give L closer scrutiny before supporting it.

Book recommendations are not a formal debate.  So, I am not sure commenter X on my blog was technically guilty of an ad hominem or not. (He seemed rather to attribute guilt by association–another fallacy–in dismissing Y’s recommendations because of Y’s admiration for Z.)  We listen to those whom we like about books, music, –all kinds of things–more than we do those whom we dislike. That may mean that in certain cases we miss out on some good books, music, or other advice. But it isn’t exactly a logical fallacy in the same way as an attack on a person as a means of defeating an argument would be.

Comments? Queries? Rebuttals? Is there a place for allowing character to influence how seriously we take another’s arguments? If there is such a place, when does it cross the line to actual ad hominem attacks?