"“All things are lawful,” but not all things are helpful. “All things are lawful,” but not all things build up."
Paul in his letter to the Corinthians does not refute their statement but adds onto it. In Christ there is no condemnation for sin (Rom 8:1) and no eternal punishment for laws that are broken. How can there be if Christ died for all sin and was raised for all glory? For the Christian, all things are lawful and permissible. You can do anything you want with the freedom Christ gives you. Paul acknowledges this but asks a deeper question, "Why would you?"
Those who have been touched by grace and have been shown God's favor have no need to keep on sinning. God's love and kindness leads them to repentance (Rom 2:4), no longer his righteous judgments. In our new found freedom, we are free to pursue relationship with God without consequence. That is the gift of grace and of the cross of Christ. No longer must we fear stumbling, but we can boldly approach the throne of grace without fear of reproach. If you died with Christ, Sin has no hold on you and death has lost it's power. Don't you believe it?
Do not ask "If Jesus paid it all, why can't I go on sinning?" If you truly believed Jesus paid it all, you know why. Don't waste your time sinning when there is a harvest to gain and treasures to store up in heaven.