Karma is really about rewarding or punishing an author for content, to encourage certain types of content. Comments that are too aggressive will not be upvoted even if people agree with the point, because they don't want to reward aggressive behavior [...] This is nonsensical in this format, but the instinct is preserved.

Karma can be (and by your own admission, is) about more than first-order content. Excessively aggressive comments may not themselves contain objectionable content, but they tend to have a deleterious effect on the conversation, which certainly does affect subsequent content.