What reasoning is present when a decision excludes someone based on unfounded beliefs about their fit within a group?

The reasoning present when a decision excludes someone based on unfounded beliefs about their fit within a group is rooted in prejudice. Prejudice involves preconceived opinions or judgments about a person or group based on characteristics such as race, gender, ethnicity, or other traits without any factual basis or evidence. This often leads to discrimination and exclusion, as decisions made on these grounds do not consider the individual's actual capabilities or qualifications.

In contrast, the other options do not align with the concept of exclusion based on unfounded beliefs. Causal simplification refers to the reduction of complex issues to overly simplistic explanations, radicalism involves extreme views or practices that advocate for fundamental changes in society, and academic detachment is about maintaining a neutral stance in scholarly debates without personal bias. These concepts do not specifically address the idea of exclusion based on false beliefs about someone's fitting within a group, making prejudice the most appropriate choice.