That's because part of education is learning to think critically, which specifically means learning to overcome those biases you mention. You say "in reality" as if those supporting education are't aware of human nature, but it's precisely because they are aware that they want people to be better educated, it helps overcome the petty tribalism inherent to the uneducated.

You're incorrect about what it presumes; valuing facts is something most people need to be taught. That's why there's always a push for education, otherwise you end up with Trumpism.