“Heresy four: There are those who believe that the doctrine of salvation for the dead offers men a second chance for salvation. This is false, false, false!”
This is a point that has been resurrected recently by Dallin Oaks and David Bednar when they talk about the sealing being powerless for anyone who hasn't remained strictly obedient to the official checklist. The problem is that, according to early church leaders, it is the modern leaders who are perpetrating a heresy.
In August of 1843 Joseph Smith said, "when a seal is put upon the father and mother, it secures their posterity so that they cannot be lost but will be saved by virtue of the covenant of their father and mother." (The Words of Joseph Smith
Brigham Young said the children who wander "are bound up to their parents by an everlasting tie, and no power on earth or hell can separate them from their parents in eternity. (Journal of Discourses
Apostle Orson F. Whitney said, "The Prophet Joseph Smith declared - and he never taught a more comforting doctrine - that the eternal sealings of faithful parents and the divine promises made to them for valiant service in the Cause of Truth, would save not only themselves but their posterity. Though some of the sheep may wander, the eye of the shepherd is upon them, and sooner or later they will feel the tentacles of Divine Providence reaching out after them and drawing them back to the fold. Either in this life or the life to come, they will return. (Conference Report, April 1929, 110)
When Newell K. Whitney agreed to give Joseph Smith his teenage daughter in trade for eternal exaltation for himself and his family, he made Joseph put it in writing that not only he, his wife, and their daughter would be sealed up to exaltation, but also their son who was likely to leave the church if he ever found out about the bargain Joseph made of promise of rewards after death in trade for the here-and-now marriage to his sister.
It wasn't until Joseph Fielding Smith and James E. Faust that church authorities began to attach caveats and requirements to the original doctrine.
McConkie and others who share his attitude remove all of the specialness from sealing. It is powerless unless you live a near-perfect life according to church standards, which is certainly not going to be the case for those lost sheep children that Joseph and Brigham promised would be saved. Ultimately, temple work is supposed to seal everyone to their parents, but it is meaningless unless it actually forms a seal that no man can put asunder.
“The easy confidence with which I know another man's religion is folly teaches me to suspect that my own is also.” -Mark Twain
Jesus: "The Kingdom of God is within you." The Buddha: "Be your own light."