In the Book of Revelation, chapter 12, John sees a dragon whose tail draws away a third of the stars in heaven.  This dragon also fights (and looses) a war with Michael.  This dragon is finally identified as Satan.  (Rev 12:3-4, 7-9).

Through modern revelation, we learn that before the world was created, Heavenly Father presented a plan to all of His spirit children that would enable them to become like Him.  For part of His plan, he needed a Savior to come down and atone for the sins of the world.  Jesus Christ volunteered to be that Savior.  Satan came up with a different plan–he would take away choice and then no one would make any mistakes so there wouldn’t be any need for an atonement. (Moses 4:1-3).

When the dragon’s tail drew away a third of the stars, Satan convinced one third of Heavenly Father’s Spirit children that his plan was better than the Father’s plan.  Joseph Smith explained, “The contention in heaven was–Jesus said there would be certain souls that would not be saved; and the devil said he would save them all…So the devil rose up in rebellion against God, and was cast down, with all who put up their heads for him” (History of the Church, 6:314).

My point is this: the choice was never between Satan’s plan and God’s plan.  Satan’s plan removed the act of choice.  God’s plan was already initiated; the choice was whether or not to accept His plan.  Likewise, we do not choose whether or not the Atonement is performed on our behalf.  It has already happened; we wimply choose whether or not to accept its effects.