Bias towards others can sometimes be justified.
We dehumanize those different others. We demonize them. Most importantly, we reduce their portion of the pie of the available resources. When there is less food or water to go around, it really makes evolutionary sense to have a built in capacity to be biased towards those who would endanger our lives. Bias means who will live.
But human perception is easily misguided, as any magician or salesperson can attest. What happens when bias is not about limited food and water buts limited money or power? Money and power translate to the preferential treament of who will get to make the big decisions. As such, more of those would mean whose beliefs and ego will be catered to. In these cases, bias means who will thrive.
The most commonly known bias is sexism: men against women and women against men. Why have men for thousands of years believe that women would be inadequate for school and work and leadership? Simply because they were busy acting biasedly by adopting stereotypes about the inability of women. These biases didn’t mean who will survive, but who will thrive. Ironically those biases/beliefs were also justified by reasons like “those stereotypes our best chance of survival because they have always been the ‘truth’ and they always will be.” As for women against men: doing that would just make them branded “witches” or “shrews” or “sluts.” Men against women sexism is so much more hip (as decided by the wise ones in power).
So how can bias continue to be a part of life? If you simply reframe the question of “who thrives” into the matter of “who survives,” you will get public support to scale up your bias. If you promote bias by directly going with the question of “who thrives,” then you’re basically telling the world that any families or children not in your part of town (or gender or race or…..) can go to hell. Which wouldn’t look very nice.