I have a unique kinship with my Calvinist brothers. I understand their desire to exalt God as completely holy and man as depraved and in need of a Savior. My problem with Calvinism is that it cannot account for the origin of evil. I love what Calvinism hopes to do in preserving God’s sovereignty, but it doesn’t work. If anyone says there’s human freedom and they’re a Calvinist, they’ve got something misunderstood (to say we have the freedom to only sin doesn’t work either). Compatibilism is really a nice try, but it’s ultimately hard determinism:
Suppose a scientist has placed an electrode in Jones’s brain so that he can read what Jones is going to do on any occasion and can cause him to do whatever the scientist desires. Now suppose the scientist wants Jones to Kill Smith, and Jones himself, in the absence of any influence from the scientist, is deliberating about the murder. If Jones decides not to kill Smith, the scientist will activate the electrode and cause the killing, but he does not need to do so because Jones carries out the act on his own. Here Jones was free but could not have acted otherwise.
Theistic compatibilism fails with the problem of evil.
Humans must have some kind of consistent libertarian freedom (see my problem with theistic determinism).
Herein lies the problem. Before a person can commit an act of sin he must first have a desire to perform that act. The Bible tells us that evil actions flow from evil desires. But the presence of an evil desire is already sin. We sin because we are sinners. We were born with a sin nature. We are fallen creatures. But Adam and Eve were not created fallen. They had no sin nature. They were good creatures with a free will. Yet they chose to sin. Why? I don’t know. Nor have I found anyone yet who does know.
In the Calvinist’s attempt to preserve God’s holiness he destroys God’s ontology by attributing him with being the author of sin. To be fair to the Calvinist, he won’t actually say that (unless you’re Sproul Jr.) but it’s impossible to get around. There’s a difference between paradox and contradiction. I find that it’s a paradox and no one knows to be a common response. A paradox is when you begin with something and the conclusion is either unexpected or seemingly contradictory. This isn’t the case. The Calvinist is trapped in a contradiction. He is affirming God’s ontology as being wholly good whereas the logical conclusion of his initial starting point ends at God’s ontology being faulted.
I agree with a lot of what Calvinism attempts to do: how it views the atonement, the depravity of man, the ontology of God, and the preservation/perseverance of the elect. As a Molinist, I render very similar conclusions, the means by which I arrive at my conclusions are rather different. It all begins with your initial starting point: how one views God’s ontology and how one views man’s freedom both pre-fall and post-fall. There are two ways to relieve God of being the author of sin: 1) attribute humans with some kind of libertarian freedom and understand them to be the origin of their own choice to sin (not any form of determinism) or 2) explain how any agent can be absolved of responsibility by causal initiation.
 William Lane Craig, JP Moreland, Philosophical Foundations for a Christian Worldview (Downers Grove, IL: InterVarsity, 2003), 270.
 RC Sproul Jr., Almighty Over All: Understanding the Sovereignty of God (Grand Rapids, MI: Baker, 1999), 57.
 RC Sproul Sr, Chosen By God (Wheaton, IL: Tyndale, 1986) 30.