As a result of Adam’s fall and rebellion, he lost his native ability to will that which is good. “Giving over to a reprobate mind” means that God consigns mankind to live in a condition that can only be undone by the gospel. It can only be undone by a powerful, regenerative work of the Holy Spirit to renew the will, to renew the affections, and to give a new heart.
The natural man only does evil all the time from the point of view of God’s holiness. This doesn’t mean that every reprobate is as reprobate as he possibly can be; there are gradations of sin. But all of mankind is fallen. All of mankind is in a state of sin and inability, and only the gospel can liberate them from that condition.
I think that Paul is saying in
Romans 1:28 that all of mankind have been given over to a reprobate mind. And from all of mankind he chose who would believe in him, He elected them.
I think you just don't understand Calvinism.