Final answer:
A fallacy undermines an argument's credibility by introducing weak, irrelevant, or false support, distracting from the logical flow and causing the reader to doubt the author's basis for their claims.
Step-by-step explanation:
A fallacy can damage the credibility of an argument because it provides weak or false support for a claim. This could be in the form of irrelevant evidence (fallacy of relevance), evidence that is too weak to support the conclusion (fallacy of weak induction), assumptions requiring justification (fallacy of unwarranted assumption), or distractions from the main argument (fallacy of diversion). For example, the fallacy of relevance includes an appeal to emotion, which wrongly leverages feelings to persuade, rather than presenting solid evidence. Utilizing fallacies limits the logical strength of an argument and can lead readers to question the author's credibility, undermining the overall effectiveness of the argument.