Why is it so important to know and avoid the most common logical fallacies?
1) You have an obligation to your readers to be fair in your arguments. And by being fair, your readers will respect you all the more.
2) If you write a persuasive article on a subject and use a common logic fallacy, the discovery of that fallacy, by just a single reader, can destroy your argument and your credibility. It implies that your argument cannot stand on its own merits, and that you are the type of person who will cheat in order to win.
3) There are unethical writers out there who know their logic cold, and who still use fallacious logic as a tactic of persuasion. They think their readers won't notice. Don't let them get away with it.