Mormons CANNOT accept that simple fact.
The "great work" that the mormon church does in their temples depends upon the "requirements" (ie. baptism, endowments, sealing for eternity, etc.) being performed for the dead, as well as the living.
The aim of the membership of the LDS church is to be "temple worthy" in order to take part in these rituals which are a necessity in order to gain "exaltation". Temple "worthiness" requires obedience and bowing to LDS authority as seen in these questions for acquiring a "temple recommend":
1 Do you have faith in and a testimony of God the Eternal Father, His Son Jesus Christ, and the Holy Ghost?
2 Do you have a testimony of the Atonement of Christ and of His role as Savior and Redeemer?
3 Do you have a testimony of the restoration of the gospel in these the latter days?
4 Do you sustain the President of the Church of Jesus Christ of Latter-day Saints as the Prophet, Seer, and Revelator and as the only person on the earth who possesses and is authorized to exercise all priesthood keys? Do you sustain members of the First Presidency and the Quorum of the Twelve Apostles as prophets, seers, and revelators? Do you sustain the other General Authorities and local authorities of the Church?
5 Do you live the law of chastity?
6 Is there anything in your conduct relating to members of your family that is not in harmony with the teachings of the Church?
7 Do you support, affiliate with, or agree with any group or individual whose teachings or practices are contrary to or oppose those accepted by the Church of Jesus Christ of Latter-day Saints?
8 Do you strive to keep the covenants you have made, to attend your sacrament and other meetings, and to keep your life in harmony with the laws and commandments of the gospel?
9 Are you honest in your dealings with your fellowmen?
10 Are you a full-tithe payer?
11 Do your keep the Word of Wisdom?
12 Do you have financial or other oblgations to a former spouse or children? If yes, are you current in meeting those obligations?
13 If you have previously received your temple endowment:
Do you keep the covenants that you made in the temple?
Do you wear the garment both night and day as instructed in the endowment and in accordance with the covenant you made in the temple?
14 Have there been any sins or misdeeds in your life that should have been resolved with priesthood authorities but have not been?
15 Do you consider yourself worthy to enter the Lord's house and participate in temple ordinances?
Pay attention to No. 14: "Have there been any sins or misdeeds in your life that should have been resolved with priesthood authorities but have not been?
"Sins and misdeeds" are to be resolved with men.
I believe that my sins and misdeeds are to be resolved by a MUCH higher authority.
4 Do you sustain the President of the Church of Jesus Christ of Latter-day Saints as the Prophet, Seer, and Revelator and as the only person on the earth who possesses and is authorized to exercise all priesthood keys? Do you sustain members of the First Presidency and the Quorum of the Twelve Apostles as prophets, seers, and revelators? Do you sustain the other General Authorities and local authorities of the Church?
Isn't amazing that there is always more prophets around in the LDS to succeed the ones that have moved on. I mean even in God's hey day prophets were rare, but now we have a whole parade of them, who just so conveniently happen to be both mormons and in the chain of command of the LDS...
And then there is:
10 Are you a full-tithe payer?
Oh yeah, got to keep the bill paid to get into heaven.Maybe even have a good credit rating as well, I think I saw something about that in Paul's letter to the Bank of Rome...