More often than not classes & meetings take a lot of effort.  Below are reasons why.

Here are just a few fallacies:
1. Ad hominem: Attacking the character of the person forwarding an argument.
2. Ad populum: Making an argument based on popular viewpoints, which does not verify it as correct.
3. Anecdotal evidence: Use of special cases to contradict an argument based on statistical evidence.
4. Appeal to authority: Argument or suggestion claiming validity due to an expert or authorities approval/agreement.
5. Appeal to ignorance: Suggesting that due to a lack of evidence for or against a case, then the case must be false.
6. Biased Evidence: Backing only one’s own opinion without investigating around the topic.
7. Repetition: Stating things in repetition does not validify a statement.
8. Straw man arguments: Misrepresenting a position, so as to create a debating point that detracts from the main topic.