How can people do such awful things?

I ask myself sometimes how people can do such awful things to one another. Joseph Smith summed it up nicely:

"All persons are entitled to their agency, for God has so ordained it. He has constituted mankind moral agents, and given them power to choose good or evil; to seek after that which is good, by pursuing the pathway of holiness in this life, which brings peace of mind, and joy in the Holy Ghost here, and a fulness of joy and happiness at His right hand hereafter; or to pursue an evil course, going on in sin and rebellion against God, thereby bringing condemnation to their souls in this world, and an eternal loss in the world to come."