In Neanderthal times, everyone in the tribe looked alike. Any one or anything that wasn’t familiar was determined a threat. The thinking process was very crude and reactionary. Everything was based on fear and survival. This is what people revert to when they are prejudiced.
There is no use in trying to convince people of the present reality that all are equal. It just creates an anger in them of past injustices and mourning a simpler time. But if enough people understand that prejudice originates in the primal brain, maybe they can shift into the awareness and freedom of equality.