We move from one of the most biblically substantiated points of Calvinism to the least.
Limited atonement is the idea that salvation is not for all people, but only for those whom God has chosen. This makes sense with the logic of Cavinism. If all salvation is based on God's sovereignty, and it is effected by God's choice, then it is only logical that not all have the opportunity of salvation, but only those who are chosen originally.
But this idea is opposed by the biblical text. The second most quoted Bible passage in the world (the Lord' Prayer is first) clearly teach this: "For God so loved THE WORLD that He gave his only begotten Son that WHOSOEVER believes in Him should not perish but have eternal life." (John 3:16, in case you didn't know).
Titus 2:11 says that God's grace and salvation is for all humanity.
Romans 5:18 says that all men are condemned, but that all men could be justified.
There are many passages like these, which confirm that while all humanity will not be saved, yet all humanity at least has the opportunity for salvation. Jesus didn't die for a few select people, but for all humanity. This is how Jesus is a new Adam, creating a doorway for all humanity to participate in a new life.
So how could formal Calvinism get something so wrong? Especially because Calvin was so biblically oriented? Because the logic of theology is so easy to be misled.
God is famously quoted as saying, "My ways are not your ways, nor are my thoughts your thoughts." This doesn't mean that God's plans for humanity can't be tracked or considered by human beings. Rather, it means that we have to rely carefully on God in order to understand God's thoughts. The problem with theology comes when we are considering our own thoughts about God instead of God's thoughts about His plans.
Frankly, we know nothing about God. We don't know God's plans. We don't know how God works. God's work is logical and it makes sense, but we have to allow God to tell us how He works and stop trying to figure it out ourselves.
Sure, it's fun to try to understand God's thoughts. Cool speculation is fine. But the reality of God is only to be supported by the word of God only. The rest of it is in the realm of fiction. The Real of reality is based only on what God says, not on our speculations.
God save us from normalizing our speculations.