The most common answer here will be: evil must be allowed to have free will. This is simply not true. If we are speaking of an omnipotent God that created the entire universe and any extra dimensional space we can't observe, then couldn't he have come up with something better?
If not, and the presence of horrible evils was the only way free will could exist, then why have horrible evils, which causes horrible things to happen to your people (eg: Babies being raped to death, mass genocide, beheadings, starvation etc.)?
Wouldn't a God that cared about his people realize that free will is not worth the mass destruction caused by the human race? Not to mention such atrocities as disease, which is not a necessary component for free will's existence, that also flourishes in this environment here on earth. What is its purpose? The questions asked here are rhetorical; the main question stands.