Thank you for writing this post. This is a phenomenon I’ve also noticed, and it applies not just to arguing but to anything to do with reasoning about groups of people. Mistakes of the type “mistakenly attributed characteristic of group to person” are common. As you said in a comment, the way that we group people is usually very lossy. This is especially frustrating for those who have to deal with the same mistaken assumption being made about them often. Making inferences about specific people based on group generalizations is useful sometimes, but acting on them wrongly often has steep costs in misunderstanding and conflict. It’s good to be reminded to keep close track of where you’re making this type of inference.