Calvinist, R.C. Sproul, writes: “If there is one single molecule in this universe running around loose, totally free of God’s sovereignty, then we have no guarantee that a single promise of God will ever be fulfilled. Perhaps that one maverick molecule will lay waste all the ground and glorious plans that God has made and promised to us. ... If we reject divine sovereignty then we must embrace atheism.” (Chosen by God, pp.26-27, emphasis mine)
Calvinist, Charles Spurgeon, states: “According to the freewill scheme the Lord intends good, but he must win like a lackey on his own creature to know what his intention is; God willeth good and would do it, but he cannot, because he has an unwilling man who will not have God’s good thing carried into effect. What do ye, sirs, but drag the Eternal from his throne, and lift up into it that fallen creature, man: for man, according to that theory nods, and his nod is destiny. You must have a destiny somewhere; it must either be as God wills or as man wills. If it be as God wills, then Jehovah sits as sovereign upon his throne of glory, and all hosts obey him, and the world is safe; if not God, then you put man there, to say. ‘I will’ or ‘I will not; if I will it I will enter heaven; if I will it I will despise the grace of God; if I will it I will conquer the Holy Sprit, for I am stronger than God, and stronger than omnipotence; if I will it I will make the blood of Christ of no effect, for I am mightier than that blood, mightier than the blood of the Son of God himself; though God make his purpose, yet will I laugh at his purpose; it shall be my purpose that shall make his purpose stand, or make it fall.’ Why, sirs, if this be not Atheism, it is idolatry; it is putting man where God should be, and I shrink with solemn awe and horror from that doctrine which makes the grandest of God’s works—the salvation man—to be dependent upon the will of his creature whether it shall be accomplished or not. Glory I can and must in my text in its fullest sense. ‘It is not of him that willeth, nor of him that runneth, but of God that sheweth mercy.’” (God’s Will and Man’s Will)
In other words, if you believe that God gave man a Free Will (beginning with Adam & Eve), then you might as well be an Atheist. Of course, then, Calvinists have no explanation for why Adam and Eve fell in the first place:
Calvinist, R.C. Sproul, writes: “But Adam and Eve were not created fallen. They had no sin nature. They were good creatures with a free will. Yet they chose to sin. Why? I don’t know. Nor have I found anyone yet who does know.” (Chosen By God, p.31, emphasis mine)
In terms of Atheism & Free Will, consider the following:
In other words, Free Will is rejected by both Determinists [Calvinists] and Atheists.