[grellas]

In law, when logic does not favor your client's position, you are trained to attack in illogical ways that still might win, e.g., appeal to prejudice, attack the person, distort the issues through (subtle) misrepresentations (crude ones being too easily exposed). It can be wearying to listen to this sort of thing being endlessly paraded before any advocate's forum to the detriment of both truth and logic.

This piece gathers and reasonably explains a useful grouping of logical fallacies. Among them: (1) Begging the question ("petitio principii"): "This is the fallacy of assuming, when trying to prove something, what it is that you are trying prove" (for more, see http://en.wikipedia.org/wiki/Begging_the_question); (2) Tu quoque ("So's your old man"): "This is the fallacy of defending an error in one's reasoning by pointing out that one's opponent has made the same error."

[timwiseman]

It seems that that would be a natural outgrowth of the adversarial system. If your goal is to persuade people and not to find the truth, then it is rational to use any ethical technique available to do so. A more inquisitorial system would largely be able to avoid this issue, but of course it creates issues of its own.