Mormons have been cursed for not following the Book of Mormon:

54 And your minds in times past have been darkened because of unbelief, and because you have treated lightly the things you have received—
55 Which vanity and unbelief have brought the whole church under condemnation.
56 And this condemnation resteth upon the children of Zion, even all.
57 And they shall remain under this condemnation until they repent and remember the new covenant, even the Book of Mormon and the former commandments which I have given them, not only to say but to do according to that which I have written— (D&C 84:54-57, 1832)

This is a CHURCH WIDE condemnation. The only way to get out from under this curse is to  come out from among them by officially having ones name removed from the records of the church.

David Whitmer Testimony

I am not judging as to the authority of any man now in the Church of Latter Day Saints, as I have told you in years past, you doubtless have authority to act in your church. But the Lord has made it known to me that the CHURCH OF CHRIST is another church, and that no man has authority to officiate in the ordinances thereof, without coming into it according to the gospel of Christ. You say, “He, (I) then and there laid down and voluntarily surrendered his (my) authority by so withdrawing.” — If this be the case, then the three Nephites lost their authority by withdrawing from the church which had gone into error and blindness. Likewise Nephi, whom God commanded to withdraw from his brethren because of their wickedness. But we see their authority was still good, although they were commanded to come out and be separated from among their brethren who were in transgression. I withdrew from “THE CHURCH OF LATTER DAY SAINTS;” I have been worshiping God in the CHURCH OF CHRIST ever since. I objected when they changed the name of the church, and always did hold to the name which Christ gave to us in 1829 — THE CHURCH OF CHRIST. (David Whitmer, “An Address to All Believers in the Book of Mormon” 1887, p. 2)

He that knoweth to do good, i.e. to leave, but who pathetically, apathetically stays, is in sin. See James 4:17.