"Is God willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil? Is he neither able nor willing? Then why call him God?"
My two cents. If god exists and there is evil and this being is god as defined by Christianity, then according the the Epicurean Paradox, god is malevolent. If god is malevolent, then god desires evil. Thus evil exists.
My problem with the Epicurean Paradox in this argument is that you are basically saying that if people do not actively attempt to stop "evil" (which is in itself a highly subjective word) then they are malevolent. This is untrue.
Using the Epicurean Paradox all of us here are malevolent as we are not stopping "evil" that we know exists in the world. We don't actively work towards the destruction of "evil" so we must be "evil" as we allow it to continue. We should not get a free pass on being malevolent just because we can't wave our hands and "fix it" like God/god can.
Personally I've never liked these types of debates, as I feel it either elevates Man far beyond his stature while at the same time lowering God (or a god or whatever you believe) to a mortal level. This argument raises Humans up to being the center of the universe, but brings God down to being just a security guard not doing a job.
The better question isn't why does God allow "evil" but why are we, as a species that is so willing to elevate itself to stand on par with God, not above preforming "evil" acts?
I'd rather have that answer any day of the week.
For the same reason a parent gives their child a new privilege and then takes it away if they cannot handle it? (Returning it when they can of course.)
A pretty weak example, as without current social constructs parents would be unable to take away a privilege. A child could also still explore a revoked privilege just not under the direct eye of the parent.
But using your example, what if Humanity has already proven to God that they can handle the privilege of Free Will? What if, despite the horrific, Evil acts that humanity has done over our very brief time in the cosmos, we have shown a supreme being that we have a far greater (or even an infinite) capacity to do Good?
Shouldn't that argument hold as much weight?