In my ideal world,

religion would cease to exist and therefore would not create an invincible boundary between mankind because that is not what religion should do. If god should exist, only one should. God's existence should also (for fucks sake) be clear-cut and not painfully ambiguous so there would be no room for doubts and questionings. No one would be able to claim that their god (or whatever their religious beliefs are) being more divine than another.

good things like food would not make you fat but ugly things like hatred, jealousy, racism would. That way people can be judged based on their looks. Knowing how humans are such narcissistic beings, we would go all out to make ourselves look good. But instead of spending a monumental amount of money on beauty and slimming fads, everyone would only need to strive to be better people. Manipulative and corrupt politicians would all turn obese and they get to die a slow painful death together.

and all children would live to see no pain and violence but only undying love and care.