Often, people wonder how there can be so much evil if God exists. But those who reject God because of evil have to borrow the biblical concept of good and evil in order to know evil exists. Simply put, the existence of evil is proof since God is the standard of good. God can exist without evil, but evil cannot exist without God. Evil is like rust on metal. You can have metal without rust, but you cannot have rust unless there’s metal. Evil is only realized and seen in the context of good. That is why when something evil is done, we call it immoral, unjust, or dishonest. 

So, evil doesn’t disprove the existence of God. It actually points to an objective good that exists in this world, because we all recognize objective evil (murder, rape, etc.). Therefore, there has to be objective good. And if there is objective good, then there’s a God.