Hostile Illusion Bias

The Hostile Illusion Bias is a cognitive bias in which a person presupposes a number of faulty premises, conclusions, or character traits in an opponent or concept and proceeds to attack the fantasy version instead of addressing the reality. This is a common occurrence, and is caused by the person making a number of unsupported assumptions, which become the object of their attacks.

This effect differs from the simple act of making faulty assumptions in that the person proceeds to attack the fantasy they've created in their mind, expending substantial energy on what amounts to nothing. It is akin to them creating a straw man, only they attack it themselves instead of hoping for the other person to take the bait.

Examples

 * Peter assumes all members of the armed forces who are sent to war must enjoy killing, and prepares an argument based on this faulty premise where he can deride veterans for being war criminals. He attacks the version of them he has manufactured in his head, rather than waiting to see who the individuals really are.
 * Sarah's boyfriend doesn't respond to her text messages in a timely manner, so she spends all day assuming the reason is because he doesn't like her or value her, or that he must have been out with another woman. She cannot wait to scold him. She will attack him and the fantasy version of events, rather than dealing with the reality of the situation, which could have been that his phone died, or that he was in a meeting, or that he didn't have service.