Listen long enough to any group of humans talking, and you're likely to hear an argument of some kind. It may be a small argument or it may be a loud and angry argument, but either way, it will very likely nucleate about a disagreement between the parties about some aspect of reality. After all, if all parties involved in an argument agreed with each other on their assessments of reality, there would be nothing to argue about. In much of our arguments, then, we should expect that our goal is to impress upon our peers that some claim is true and correct.
This process of disagreement and ensuing debate are thus potentially good and useful: to the extent that we are only convinced by logically and empirically sound arguments, then debate furthers our understanding of the world. Implicit in this assessment, however, is an assumption that both parties are actually interested in the pursuit of truth. That is, arguments are useful only insofar as the parties to an argument are practicing good faith.
If one is honest about their arguments, then that must necessarily include an understanding that they could be wrong and hence that they could "lose" an argument. Thus, one can violate good faith by disallowing for any change in their views as the result of an argument. This violation is especially common in discussions about religion, where one party to an argument (typically the more religious party) refuses to admit of any evidence or line of reasoning which could possibly budge them from their beliefs. It is simply not plausible that any individual human is infallible, even within some particular domain of knowledge, and so to argue from infallibility is to deny that one's understanding of the world could possibly be more complete. Such a denial is fundamentally incompatible with the goal of learning, and hence has no place in a discussion intended to bring enlightenment.
In a similar vein, good faith requires that one only advance arguments that they do not already know to be false. If someone shows that your argument is not in correspondence with reality, then continuing to use that argument is an affront to the pursuit of understanding and of truth. To be particularly blunt, the use of known-false arguments is simply dishonest, and is the practice of a liar.
It is concerning ourselves with good faith that we find it important to be aware of common logical fallacies. It hardly does anyone any good if an argument is tainted by mistakes which have been well-understood for centuries to be flawed. Appeal to authority, post hoc ergo propter hoc and confusion between correlation and causation, to name a few examples, should all be seen as undermining an argument and hence avoided.
On the other hand, it is similarly unconstructive to bludgeon others with a mistaken understanding of some particular logical fallacy, such as the ad hominem fallacy, that favored bludgeon of those arguing from bad faith. ("What? You called me a clueless gobshite? That means I won!") Focusing on name-calling, ridicule and other such patter comes at the cost of focusing on the merits of an argument. Taken to its extreme, critiquing a lack of decorum represents bad faith in that it distracts from critical evaluation of an argument. Of course there is a point at which a stream of ridicule or a particularly vile insult also disrupts useful debate; I call it a failure of good faith when this valid concern is exaggerated and perverted for the purposes of distraction or suppression.
Perhaps the most common and hence egregious violation of good faith, however, is the intentional mischaracterization of another's opinions for the purpose of delegitimizing their views. While there is room, of course, for arguing that one's opponent is being dishonest in how they describe their views, there is a wide gulf between such arguments and flat-out lying about what someone else does or says. By lying and employing such strawmen, one once again gives up discovering what is true. To wit, fighting a strawman doesn't expose holes in an argument, but rather is a strategy explicitly purposed to prevent having to change one's views in the face of opposition. Such dishonesty is by nature incompatible with reasoned and constructive debate, and should be disdained as strongly as any other form of blatant dishonesty.
Why is good faith so important to me, though? Because I actually care about learning more about the world. Because engaging someone in an well-reasoned argument is time-consuming, and should be reciprocated in kind. Because we, at a societal level, desperately need constructive discourse, no matter how much popular etiquette demands that certain views be kept out of the public sphere. Because constructive dialogue is much more about intellectual honesty and mutual respect for the truth than about how many profanities are spoken. Because we, as a culture, seem to have forgotten (if indeed we ever knew) that truth is something to strive for and that dishonesty is something to hold in contempt.
I don't ask that the whole world agree with me--- that would be boring and quite useless, after all. I don't even ask that people refrain from calling me an ignorant fucktard (or whatever the slang of the day might become). I merely ask of my peers that we all engage in good faith as we seek to improve our understanding of the world.