Think about how many people end up discouraged or completely disillusioned because of what Calvinism teaches. They hear that everyone is already unchangeably eternally decreed and determined in a category. Either the saved or lost, and nothing can ever change it. If God didn’t choose you for salvation, you have no hope. Jesus didn’t even die for you. There’s absolutely nothing you can do, not even to want to do something different, because you were born with a nature that hates God and makes obedience impossible. You’re helpless to change. And then, on top of that, you’ll be condemned forever for something you never had the power to avoid. That’s deeply troubling to people. A Calvinist might say, ‘Well, that’s what the Bible teaches if you’re a Calvinist.’ I don’t believe that for a second, but regardless, that’s the practical outcome of their system.
Also, if Calvinism is true, Romans 9 would be “O man, who are you to reply against God? You’re the man who has been eternally decreed to reply against God. How dare you do what God ordained you to do from eternity? Oh, and by the way, you are going to be rebuked and eternally punished for doing what you were eternally determined and decreed to do”—all while Calvinism teaches and believes God is righteous, holy, loving and just. Can’t have both ways.
And if Calvinism is consistent, and if God unchangeably determines every thought, motive, and deed, then Calvinists can't just give him credit for the good things. They can say He may decree them in different ways and that He has a secondary means for ways for one thing and for another He decrees it differently. But He’s still unchangeably decreeing all of it. And there is no human power for any human being to do anything differently. And by the way, that would include Adam. And so, that makes him the author of sin [when you take Calvinism consistently and logically]. In Calvinism, even the first evil intention, even the one in Satan's heart, Satan had no control. He had to do it. He had to want to do it. Whatever it is, you have to be consistent. And Calvinists are inconsistent. If they are going to give God the credit for all the good things, they have to give him the credit for all the bad things, which ultimately is saying He is the author of sin, that makes Him evil [when you take Calvinism consistently and logically].