Christianity is built around the concept of Jesus' resurrection. Jesus famously said, "I am the resurrection, and the life: he that believeth in me, though he were dead, yet shall he live: And whosoever liveth and believeth in me shall never die".
You could, of course, argue that conservative Christianity is especially dependent on this concept. If Jesus' body were found tomorrow, proving beyond a shadow of a doubt that he'd never risen from the dead, liberal Christians (who don't worry too hard about the literal truth of the Bible anyway) would probably say, "Yes, but he lived a great life and taught us so many wonderful things!" But really, if Jesus wasn't resurrected, the whole religion crumbles and becomes meaningless, because Jesus' supposed sacrifice of death and his triumphant resurrection is at the heart of Christianity. As a Lutheran, I used to recite the Apostles' Creed every week, including these words (this is from the "green book," the LBW, which does not quite match the current version listed on the ELCA website):
I believe in Jesus Christ, his only Son, our Lord.
He was conceived by the Holy Spirit
and born of the virgin Mary.
He suffered under Pontius Pilate,
was crucified, died and was buried.
He descended into hell.
On the third day he rose again.
He ascended into heaven,
and is seated at the right hand of the Father.
He will come again to judge the living and the dead.
How exactly does a "resurrection" happen? Well, the Bible tells us that Jesus was dead-- not in a coma, not in shock, but stone dead-- and yet when the tomb was opened days later, he was quite alive. Is this possible? Of course not. By that time, Jesus would have been well and truly brain dead. Wikipedia defines "brain death" thusly: the irreversible end of all brain activity (including involuntary activity necessary to sustain life) due to total necrosis of the cerebral neurons following loss of brain oxygenation.
Notice the term "irreversible" in there. I'm no doctor, but if you don't breathe, your brain stops getting oxygen, the neurons stop functioning, and within four to six minutes your brain will no longer be of any use. After two days, fairly substantial decomposition of the body would have set in (don't follow the link if you don't want to know the gross details). In short, poisons build up inside you and your cells begin dissolving from the inside out, and after two days of death the rest of your body wouldn't be of much use to you either. The people of that time understood this clearly; when Jesus asks for the stone to be rolled away from Lazarus' tomb, his sister objects, "But, Lord, by this time there is a bad odor, for he has been there four days."
So for Jesus to be resurrected, God would have to reverse the decay of the body, repairing all those cells that were already destroyed internally, and to restore functioning to long-dead neurons as well. How did he do this? How could he have done this? Saying "it was a miracle" is inadequate. It defies everything we know about medical science and the body. It simply can't be done. A two-day-old corpse is very, very dead, and can't be reanimated.
So why do we pretend this is a reasonable tenet of the Christian faith, when it's clearly absurd? Why do we even admit that it might be a possibility, when it is so clearly not? It's a myth, no more likely to be the truth that the birth of Athena from the splitting of Zeus' skull, and as such it doesn't really deserve to be danced around and given tacit acceptance as a reasonable idea. As Robert A. Heinlein rather unkindly put it: "'But you must respect another man's religious beliefs!' For Heaven's sake, why? Stupid is stupid--faith doesn't make it smart."
I will say I'm not quite as bluntly rude as Heinlein was. If people want to believe in silly things, that's their prerogative. I believed them myself for a while, and I know that reasonable people can believe unreasonable things. But when people come proselytizing to my door, or ridiculous beliefs become the basis for public policy, I don't have a problem with pointing out that the emperor has no clothes, and that Jesus cannot possibly have been resurrected from the dead. Why pretend it's a reasonable belief, when it's not?