If we have the opportunity to accept the gospel, and we refuse it, we come under condemnation. If we refuse the message, we have refused the gift of the atonement. It cannot fully apply to us if we do not fully accept it.
Reference: The phrase “better for them if they had not been born” is seen in a particular context in both the New Testament and the Doctrine and Covenants.
Mark 14:21
21 The Son of man indeed goeth, as it is written of him: but woe to that man by whom the Son of man is betrayed! good were it for that man if he had never been born.
Doctrine and Covenants 76:32-33
32 They are they who are the sons of perdition, of whom I say that it had been better for them never to have been born;
33 For they are vessels of wrath, doomed to suffer the wrath of God, with the devil and his angels in eternity;
For both Mark and DC 76, the phrase idea that one would be better never having been born is related to the worst possible scenario. Specifically, it is the sons of perdition in the Doctrine and Covenants, and Judas as betrayer is considered to be one of the sons of perdition. The fate of a son of perdition is to undergo the second death, and to fail to be redeemed at all by Christ’s atonement.
“The atonement of Jesus Christ ransoms and rescues all mankind, without exception, from both deaths brought by the Fall of Adam. This means that every person will die physically and every person will be resurrected physically from the grave and be given everlasting life. In like manner, every person, regardless of worthiness or unworthiness, will also be reclaimed from the spiritual death and will be brought back into the presence of God for the Final Judgment. No matter how wicked or unrepentant, every person will, after the Resurrection, be brought back into the presence of God for judgment. Thus all will be reclaimed from the two deaths that resulted from the fall of Adam. Those who are righteous will remain in his presence. Those who are still unclean and filthy at the time of judgment will be sent away from his presence a second time, and thus they die a second spiritual death. Only the sons of perdition suffer the complete second death. This is clearly detailed by Samuel the Lamanite in Helaman 14:15-18, by Moroni in Mormon 9:12-13, and by the Lord in D&C 29:40-44 and 76:37-38.” (Monte S. Nyman and Charles D. Tate, Jr., eds., Alma, the Testimony of the Word [Provo: BYU Religious Studies Center, 1992], 55.)
It is this context of failure to have the atonement apply that allows us to see the context in which Mormon is using the phrase “it would be better for them if they had not been born.” He does not appear to be specifically discussing the sons of perdition, but rather any who reject the Atoning Messiah. In symbolic terms, they have rejected the Savior by not “receiving” him, and therefore they reject the opportunity to receive the benefits of the Atonement. Certainly anyone who could not have the benefit of the atonement would fit into the category of one who would be better having never been born. Nevertheless, even though the terms are similar, Mormon is certainly not intending to discuss the technical category or sons of perdition.