According to open theism, God has sovereignly decided to create a world with libertarianly free creatures and, since there are no true (would-) counterfactuals of creaturely freedom for God to know and since, according to open theists, libertarian freedom is incompatible with meticulous foreknowledge, God could not know for sure ahead of time what kinds of choices his free creatures will make. God would seem to be less blameworthy for not preventing evils that he didn’t know in advance would happen.
i) In human affairs there are situations where ignorance can be an extenuating or exculpatory factor. But that's not a given.
Suppose I leave the house for an hour to go for a walk. I leave my young sons–ages 2 and 3–alone with a space heater running. In my absence the house catches fire and they burn to death.
I didn't know in advance that this would happen. But that misses the point. It was reckless of me to expose them to gratuitous risk. It was wrong of me to take that gamble at their expense. In fact, even if the house hadn't caught fire, I'd still be negligent, still be culpable, for endangering them.
ii) This assumes that God is, in fact, ignorant future evils. But surely that's overstated, even on open theist assumptions. Suppose the open theist God didn't know 3 days in advance that the Titanic was going to hit an iceberg and sink. Maybe that was contingent on a string of unforeseeable human choices.
But did the open theist God still not know 3 hours in advance that the Titanic was going to hit an iceberg? Could he not even anticipate 30 minutes in advance that the Titanic was on a collision course with the iceberg–given the trajectory? How much lead time does it take to swerve?
And even if that wasn't a "sure thing," is it not responsible and prudent to take precautions just in case? Especially when innocent lives are at stake? If God can't know for sure, isn't that all the more reason to leave himself a generous margin of error?
iii) Likewise, didn't the open theist God know that category 4 hurricane was making a bee line for Galveston? Can't the open theist God predict when and where a hurricane will make landfall at least as well as the National Weather Service?
iv) At this point an open theist might counter that even though God can anticipate some (all?) natural disasters, God can't intervene to prevent them. For human choices to be meaningful, choices must have predictable consequences. That, in turn, requires a stable environment.
However, that reply is subject to multiple objections:
v) To begin with, the open theist is suddenly shifting ground. This argument concedes that divine ignorance is an inadequate theodicy.
vi) A stock objection that open theists raise to Calvinism is that if every event is predestined, then petitionary prayer is otiose, for the future is written in stone.
(Of course, in Calvinism, the stony inscription includes answered prayer.)
If, however, God can't destabilize the natural order by overriding the default setting, then open theist theodicy negates open theist prayer.
vii) Furthermore, the argument backfires. If choices must have predictable consequences, then choices require informed consent: permission granted in the knowledge of probable risks and consequences.
If the residents of Galveston had known that a catastrophic hurricane was going to hit their town on Sept. 8, 1990, many of them would evacuate ahead of the storm. And even if some stubbornly remained behind, that would be their informed choice.
However, the open theist God withheld that information. They had no advance warning, to make preparations.
This doesn't require God to divert the hurricane, but simply forewarn the residents. The natural order remains inviolable.
Suppose I suffer from migraine headaches. I consult a neurologist. He says I'm in luck. He can prescribe a medication that relieves the headache.
However, he neglects to tell me that the medication has a side-effect: it causes brain cancer.
Although I chose to take the medication, I was denied the opportunity to make an informed choice. Had I known the side-effect, I would not have taken the medication. The neurologist was guilty of malpractice by failing to warn me.