We are constantly reminded about the destructive consequences of religion -- intolerance, hatred, division, inquisitions, persecutions of "heretics," holy wars. Though far from the whole story, they are, nevertheless, true. There have been many awful consequences of religion.
What one almost never hears described are the deleterious consequences of secularism -- the terrible developments that have accompanied the breakdown of traditional religion and belief in God. For every thousand students who learn about the Spanish Inquisition and the Salem Witch Trials, maybe two learn to associate Gulag, Auschwitz, The Cultural Revolution and the Cambodian genocide with secular regimes and ideologies.
For all the problems associated with belief in God, the death of God leads to far more of them.
So, while it is not possible to prove (or disprove) God's existence, what is provable is what happens when people stop believing in God.
1. Without God there is no good and evil; there are only subjective opinions that we then label "good" and "evil." This does not mean that an atheist cannot be a good person. Nor does it mean that all those who believe in God are good; there are good atheists and there are bad believers in God. It simply means that unless there is a moral authority that transcends humans from which emanates an objective right and wrong, "right" and "wrong" no more objectively exist than do "beautiful" and "ugly."
2. Without God, there is no objective meaning to life. We are all merely random creations of natural selection whose existence has no more intrinsic purpose or meaning than that of a pebble equally randomly produced.
3. Life is ultimately a tragic fare if there is no God. We live, we suffer, we die -- some horrifically, many prematurely -- and there is only oblivion afterward.
4. Human beings need instruction manuals. This is as true for acting morally and wisely as it is for properly flying an airplane. One's heart is often no better a guide to what is right and wrong than it is to the right and wrong way to fly an airplane. The post-religious secular world claims to need no manual; the heart and reason are sufficient guides to leading a good life and to making a good world.
5. If there is no God, the kindest and most innocent victims of torture and murder have no better a fate after death than do the most cruel torturers and mass murderers. Only if there is a good God do Mother Teresa and Adolf Hitler have different fates.