What's the one problem facing the world you'd wish to end?

the Pokemon Go game... it needs to go away before the entire world is hopelessly addicted

The problem is one of a crisis in consciousness to which we've been trained into acclimation. All those things you list, and more like them, are simply expressions of it. Trying to end these expressions is an exercise in futility, while further hiding and allowing the crisis in consciousness to strengthen. We need to address the crisis BEHIND these expressions, not simply see the expressions as the problems themselves.

Ignorance.

@Carver Ending religion... A way to destroy a lot of hatred, based around a random system of beliefs. The only consequence I can see is the good culture religion can represent

Greed, Many problems
stem from that alone.

Religion

@sophrai good point

lack of education