Will Duffy, from a Facebook conversation:
When a Calvinist says that an unregenerate man is free to sin, he is lying to you. No Calvinist in the world believes that an unregenerate man is free to sin. An unregenerate man cannot sin unless God decreed for him to sin. An unregenerate man cannot freely choose what sin he wants to commit, he can only commit the sins God decreed for him to commit. According to Calvinist doctrine, God is the author of sin, not man. Man has no say in the matter.