I believe the world is getting better. The material evidence is all around us, as I have written before.
I believe that God guides the general direction of the world with a providential hand.
Most of the writers who share my belief that the world is getting better seem to atheists who believe in naturalistic evolution.
If you are a naturalistic evolutionist who does not believe the world is getting better, then you have no problem - species simply adapt to whatever the environment happens to be at the moment, without direction or meaning. The world is neither getting better nor getting worse, because there is no naturalistic meaning to those terms when applied to all existence. Evolution is simply change over time.
But naturalistic evolutionists who do believe in progress have to go through some elaborate twists to explain both why our evolutionary practice seems to show a positive design without a designer, and how we keep progressing even though our evolved psychology is pessimistic.
It seems to me that theistic evolution is a simpler account of how a species designed for both hope and fear, designed for pessimistic assumptions but optimistic actions, can in fact achieve such progress.
I don't have an elaborate philosophical argument here. I just think that people who see that the world is improving through the amazing collective action of creative humans are halfway to seeing that we are meant for this by a Creator.