The problem of evil falls into two parts: human evil and natural evil. The term “natural evil” describes disease, natural disaster and similar occurrences. The term “human evil” describes things like terrorist acts, murders, rape, genocide, and similar occurrences.
With regard to human evil, critics and skeptics often ask how, if there is a good God, he can allow such events as terrorism (e.g., 9/11), the rape and murder of children, genocide and the like to occur.
These are the same people who value human freedom and the notion that a person shapes his or her own destiny and should be unconstrained by outside forces or coercion (including God).
The inherent problem in this criticism is made obvious when the previous two sentences are laid side-by-side, namely, that one cannot desire freedom and at the same time be upset that God does not stop other people’s freedoms.
Every human being has freedom, which I will define as the ability to make moral choices that are free, that is, unconstrained or coerced by anything outside oneself.
(Note that even a Calvinist will agree with this since biblical Calvinism, despite the caricatures, teaches that a person’s sinfulness, and thus his inability to turn from sin and to trust God, stems from his own nature; no one is forced to act in a sinful manner nor is anyone restrained from coming to God by anything except his own sinfulness.)
With regard to human evil, one cannot believe in and even desire such moral freedom and then blame God when some use that moral freedom to commit atrocities.
You can’t have it both ways.