I read once that it's a social evolution thing. Humans are more likely to survive if we work together, and part of working together means following the rules and a little bit of self sacrifice. We get a little shot of dopamine when we call someone out for breaking the rules because it makes the tribe stronger. The problem is that we figured out that psychological hack and it's being exploited now to insane levels. We are wired to stop the guy next to us from eating twice his share of the crop or whatever, not for seeing every little assholeish thing some random politician said on the other side of the country, or every person a cop beats up, or every time a Karen is rude to a cashier, and so on. I don't know how accurate that is but it sure sounds right.