What they fear is that the Mormon records of the Holocaust survivors may be the only surviving records in 10,000 years. This would create a purposefully flawed archeological record that 6 million Mormons were slaughtered in the gas chambers.* The Mormons already make many unsubstantiated archeological claims already regarding ancient Christians in North America. It would be tragic for their fudged records became the only documentation of our times available in the distant future.
The Catholic Church will certainly still exist to dispute their claims, but its not inconceivable that over 10,000 years, the vast majority of documents could be lost due to failing hard drives and natural disasters consuming the paper trail. (We have certainly lost the birth certificates for Cain and Abel, born in a similar time frame ago!) All that is needed is one surviving Mormon vault to potentially cause a crisis of faith sometime in the future, based on wholly fabricated history.
- (Slaughtered by a man who himself ultimately repented and received a Mormon baptism, as they have posthumously baptized Adolph Hitler).