I consider that men are free to choose only what they are capable of doing. I'm not free to fly, other than by artificial means, because it is not yet in my ability to do (perhaps in my resurrection body it will be).
Since scripture holds that man's heart is "only evil continually" (evil being defined as anything that falls short of God's glory, including what we may call "good" - Jesus said "no one is good but God alone"), we must first be freed to choose surrender to Christ over trusting - with God-given faith - in any other means of attaining salvation.
The Apostle Paul describes the state of unregenerate men as "bound," "enslaved," "held captive," "dead," etc. Such a captive cannot choose to be liberated. He must first be liberated and then is free to choose to follow a new Master. I love the irony of Paul's description that unless one is a slave to Christ, he or she is not free at all.
I submit that only Christians have free will. The unregenerate are held captive and incapable of choosing outside of their ability.
-Robin
First, the fact that the scriptures say that every imagination of the hearts of men was only evil continually does not mean they were unable to have good thoughts and imaginations.
If I were to say that none of my neighbors ever goes to church, no, not one, does that mean they are unable to go to church? No, it simply states they have not. It does not address ability at all.
The same with Gen 6:5, the fact that the imaginations of men were only evil continually is not saying they could not think and imagine otherwise, you have assumed that.
When Paul describes us as slaves to sin, that does not mean we are compelled to sin. A slave can disobey his master, a slave can run away from his master. A slave is not a mindless robot.
What is meant is that we are held captive under the condemnation of death. Even if we do good, it does not take away the fact that we have sinned, and the penalty or wage of that sin is death. So, no matter how good you might be, you are held captive by sin. This is what is meant.
The only reason we can be saved is because when we trust Jesus we are baptized into his body. We died to sin with Jesus in his death, and we are raised together with him to righteousness. We are no longer held captive by sin, we have died to it. This is why it is also described like marriage, as long as a woman's husband lives, she is bound to him. This does not mean she cannot disobey him, yet she is bound to him by law. When he dies, she is free to marry again.
So being enslaved to sin does not mean our every thought and imagination is held captive and we are compelled to sin. But it does mean we are held captive in the condemnation of sin, which is death. We are like a man held on death row in prison, doomed to execution.