Not sure if it's a small thing but I think I would change it so good deeds make a bigger impression on people than the bad.
It's a bit of a rainbow sunshine kind of wish but it's human nature to remember bad things easier than the good, it's a survival instinct to protect ourselves. But with all these conflicts and discrimination, big or small, if people don't let fear dominate, everyone would cut each other more slack.
Of course this requires everyone to have the same mindset to work, that's why I think making that small change in human nature at its core is the only way, and only a genie could pull that off.