Benjamin, I think that perhaps you have a misunderstanding of what is being stated by many that you call "Calvinists", as in threads past.
There is no "logic" to it at all, and there never has been.
Please allow me to correct the imaginary conversation above, where I think that you're not seeing some important details:
Bill C: "God sits upon His throne and Has the final say on each and every thing that happens. He, being the sovereign master over all of creation, either permits it, or causes it, and no one can ask Him why."
Bob A: "Did God determine the things that Jeffery Dahmer did?"
Bill C: "No, but He knew what men like Jeffery Dahmer would do, because like all men, Jeffery Dahmer was deterrmined to love his sin and refuse to repent of it. In fact, the Lord gave men like him over to it and allowed them to carry out the evil thoughts and intentions of their own heart, because He had a purpose for allowing them to do so...to judge them for their sins or to forgive them for those same sins through the justifying blood of His own Son."
Bob A: " Who determined Jeffery Dhamer's nature?"
Bill C: " Both God and Jeffery Dahmer did. Jeffery Dhamer wanted his sin, and God gave him over to that which he loved more than God...men like Jeffery Dahmer didn't start out that way, but they spiraled down into it gradually, of their own free will; However, God allowing it still doesn't give Jeffery Dahmer any excuse, because he willfully sinned and loved it. God simply stood back and allowed him to do that which he wanted to do. "
Bob A: "I'm confused...aren't you saying that God made Jeffery Dahmer, knowing full-well that he would commit the sins that he did? "
Bill C: "Yes, I am. According to Romans 9:14-18, He has mercy on which rebellious sinners He wants to, and has compassion on which of them He wants to. According to Romans 9:22-24, the Lord has made some vessels for salvation, and the rest for damnation."
Bob A: " But that's not fair!"
Bill C: " For all have sinned and come short of the glory of God. There is none righteous, no not one. There is not a just man on the earth who does good and sins not. All men are without excuse. The Lord does as he wishes in the armies of heaven and among the inhabitants of the earth. Who are we to question His wisdom and judgment and for creating us? We are the ones who have sinned, each and every one."
Bob A: " I don't understand."
Bill C: " None of God's children, those who have believed on Christ from the heart, understand it all at once. It takes time for the Lord to transform the mind through His word. Just accept His words and believe them by faith, committing your understanding of it to God. Also, know that someday you can and will understand it all, by His grace. The first step is to believe the words on the page, and to not reject one iota of what is written... no matter how contradictory it may seem to you."
Bob A: "OK, what have I got to lose? God says that His word is truth and that He cannot lie...So, I can't go wrong if I believe Him and trust Him at His every word."
@Benjamin,
May the Lord bless you richly in your studies of His word, in your daily walk with Him, and most importantly...
May you always be reminded of the love that He has for each and every one of His children.