People are not reasoning logically at all — rather they are looking for a balance between costs and benefits in social exchange (“you give me X, I give you Y”), or in the calculus of social status (“you’re in social category X, so you’re entitled to benefit Y”). They’re especially sensitive to cheaters and poseurs — those who take a benefit without paying the appropriate cost, or having the appropriate status. Sometimes this sensitivity to social cheating happens to correspond to logical inference, but often it doesn’t.