Throughout the centuries, people have found justification for the mistreatment of others by pointing to the differences among each other. The point is that if what justifies equality and proper treatment is humanness and rationality, that to deny someone of such mistreatment is to deny their humanness. Therefore, those of the past justified slavery with the myth that blacks were 3/4 of a person, more like an animal, and uncivilized persons. To justify the mistreatment of women, many have pointed to their differences in comparison to men.
The reality is that there are no significant differences between people. Therefore all irrational justification of inequality is baseless. That’s why Plato allowed women to also be guardians or philosopher/kings in his republic because although he recognized differences between the sexes he realized that the ability to be a person of reason, spirit, or appetite was based on individual gifts not individual sexual differences. As much as Immanual Kant racial and prejudice views are known, it can not supersede the fact that he also argued that we are all humans with dignity, and that criteria alone demands that we are all treated as ends and not as means.
The video above is based on The Races of Mankind Pamphlet and was created in 1946 as a way to get adult workers to recognize the similarities between each other and to foster cooperation. If only we can all finally get this message through our heads, our “civilized” societies would be all the more better.