Arminians (and other Christian libertarians) typically accuse Calvinism of making God the author of sin since God decreed the fall of Adam and Lucifer. If God decreed that outcome, then they lacked the freedom to do otherwise.
By contrast, Arminians think God gave Adam and Lucifer the freedom to do otherwise. Yet, as we know, Adam and Lucifer still fell. The didn’t use their libertarian freedom to do otherwise.
Hence, the outcome is identical on either scenario. Even if God had given Adam and Lucifer the freedom to do otherwise, they would have done the very same thing.
If God decrees an outcome which coincides with a libertarian choice, then how does that action make him the author of sin? In each case, the end-result is identical.
At best, the objection would only be plausible if, given the opportunity to make a different choice, the agent would make a different choice. If, however, the agent made the very same choice, then how is the difference between determinism and indeterminism morally relevant at that juncture?
And, from a libertarian standpoint, this is true of all sins of all sinners. Don’t libertarians think that when sinners sin, they were at liberty to do otherwise? To refrain from sinning?
So even if God predestined every sin, the outcome is uniformly identical to the libertarian scheme.
For the objection to be plausible, an Arminian would have to show that predestination makes the agent do something he’d refrain from doing, if given the opportunity to do so.
Yet, as a matter of fact, the libertarian thinks that we’ve actually seen that libertarian alternative play out. We’ve seen what happens when libertarian agents make their own choices. And the indeterminist alternative is functionally interchangeable with the determinist scenario. Since the end-result is, in each and every case, the same, there’s no practical difference between the two.
If God predetermines an outcome which is identical with an indeterminate outcome, then why does that make him the author of sin?