For a number of historical and cognitive reasons, humans evolved an unfortunate tendency to do this, and in some instances it is adaptive. I eat a piece of fruit I’ve never eaten before, I get sick, I then assume (inductive reasoning) that all pieces of this particular fruit are potentially inedible. We make generalizations about entire classes of people or things because the brain is a giant inferencing machine, and it uses whatever data it has in its attempt to ensure our survival.
