People blame God for evil because they want to so trust Him to solve all their problems and wipe away evil that when this does not happen they blame God and feel He has disappointed them. It is an immature belief in God in thinking "He could have prevented this." A lot of our calamity comes from our mindsets that need to be renewed and from our sin nature. We are not created to be like robots and just accept things but to actively partake in life, so to speak and in each dimension to call upon Him for guidance.
God does not tempt us with evil but He does allow the evil to come our way to strengthen us and for us to see what is in us. He does allow people to sin so that we can exercise our free will in choosing the right or wrong path. There is always a way out of sin if we surrender. Evil is necessary as this is Satan's world we are living in and the Bible tells us that we are Ambassadors for Christ, just passing through. How else can we see the hand of God work unless He intervenes on our behalf. He does show HImself strong to those that call on HIm(2 Cor.12:9, and Jer. 33:3).