Knowledge of logical fallacies is a powerful tool for both improving your own reasoning and examining the arguments of others. Many of them seem ridiculous or absurd on their faces, but people actually do formulate and fall for arguments that use them! There are many more named logical fallacies. If this whets your appetite, Wikipedia’s list makes a good jumping-off point, and an introductory text on informal logic makes an even better one.
Testers need to reason with both computers and other people, and logic is at the heart of both. Whether analyzing the flow of a program, making a case for fixing an involved bug, or evaluating next quarter’s development plan, a solid grounding in logic will serve testers well.