This is based heavily on the following video:
When I showed this video to a Christian who was trying to re-convert me, he asked, “Is not being able to open a peanut butter jar a violation of free will?”
Here’s the difference between the questions “Is rape a violation of free will?” and “Is not being able to open a peanut butter jar a violation of free will?”: the first question necessarily deals with at least two agents, while the second deals with only one. A peanut butter jar is incapable of acting under its own agency and therefore cannot violate free will; a rapist is acting under his own agency and necessarily asserting his will over that of his victim. How is that better than god asserting his will over that of the rapist?
Further, how is stopping a child from dying of cancer a violation of free will? Is the will of the cancer cells important? Is there any person, alive or dead, anywhere who wants or has ever wanted children to die of cancer?
Here’s the thing: if all suffering everywhere had always been the result of agency, perhaps the free will argument would have a leg to stand on. But this is simply untrue. Besides, there is at least one story in the Bible where Jesus specifically acted to save the life of a woman about to be killed (John 8:1-11).
If you truly believe, as a Christian, that god does not stop rape and murder due to free will, isn’t it only consistent to believe that if Jesus were around today and saw an act of rape taking place, he would do nothing to stop the rapist?
Do you think the Jesus of the Gospels would refuse to act to save a victim of rape or murder if he saw it happening in the streets of Jerusalem?
If not, maybe you should rethink the free will defense against the problem of evil, because if an omnipresent, omnipotent god exists, he certainly has no problem allowing rape and murder when it happens in his presence.
The Complete History of the Universe: A Personal Journey 
I remember this conversation. To be honest, the question is dumb, and I can’t help but think that the person who asked it knew that it was dumb.
The free will defense for the problem of evil fails because they posit an all-powerful, omnipresent, all-knowing god that has ultimate dominion over nature. He made it, according to them, and reaching back in history they attributed many natural things to his acting on nature.
They still do that to an extent, so we can ask this: when thousands of people die from a natural disaster, why does God not intervene to stop it? Or perhaps even better: is God responsible for the natural disaster in the first place (there’s a reason, I assume, we call them “acts of God”)?
So we have a problem, here; innocent people die on account of God’s actions or inaction, taking free will from the argument. I would consider a hurricane that wipes out a city and kills thousands of people to be an act of evil if there was some kind of intelligence behind it in some way—or if it was a simple act of nature that an omnipotent and omnipresent God didn’t stop.
But your point about agent causation is important: what is stopping a person from opening a jar of peanut butter is not a trickster demigod casting a spell to make the jar unopenable, or even more reasonably, a company that intentionally designs jars that cannot be opened. What’s thwarting the attempt is simply nature. There’s no intention or agents involved beside the person trying to open the jar.
Free will, if it exists, doesn’t exist in a vacuum–it exists in certain contexts. An agent acting in a physical universe with unavoidable and predictable laws of physics will be beholden to those laws of physics by definition. That means that an agent with free will cannot simply, for instance, just choose not to be hungry, fly like a bird, or cure cancer with nice thoughts. Does a lack of water in the desert violate the free will of a thirsty person?
And I think that this exposes another issue with free will: to what extent is a person who is limited and shaped by their environments actually free? If we starve from a lack of food, it’s not always because we’ve chosen not to have food (or made choices that directly led to that outcome, say for instance if there was a severe drought).
Your comment is a great addition!
I think there is always, ALWAYS more to say about the Problem of Evil, because believers often refuse to see the problem as such. For religions like Christianity, there is simply no way to escape it without limiting god’s power… or his love.
Perhaps some Christians recognize the problem as so powerful that they would lose faith if they really were honest about the question?