This is what I get for taking the road less travelled.
The original question is here. As I began to say at the end of it, you have to assume certain premises before this discussion is even relevant:
- Jesus and the apostles actually existed and knew each other.
- Jesus was indeed crucified or otherwise publicly executed, or at least shown to be dead.
- The apostles genuinely knew whether the resurrection had happened.
- At least some of those original apostles were really martyred for saying Jesus was resurrected.
Available extra-Biblical circumstantial evidence for any of the above is sparse and contested to the point where many non-Christians hearing this question will demand more before even considering it. To see what I mean, follow the link in the other question to the forum where it first came up.
Confident that the evidence angle is thoroughly covered for the time being, I thought I'd examine whether the conclusion is valid even if one accepts the premises. I still don't think it is, because there are circumstances in which the apostles reasonably would lie and die for it. Even if my argument falls flat on its face, though, it's hardly the last remaining line of defense against this apologetic chestnut.
You say I didn't explain how Christianity benefited the first Christians. Are you implying that there is no earthly benefit to being a Christian if Christians are few and persecuted? Fine, if a Christian thinks so then I won't argue, but these particular Christians had a plan. They saw ahead to a time when other people, and the people in charge, and the entire society around them would be Christian too. Then it would be wonderful to be a Christian. Life would be so much better than when nobody was, because Jesus's teachings would help them all to live in harmony.
A Christian's loved ones shouldn't be limited to his or her family and friends. Jesus' message was supposedly to love everyone, even one's enemies. If the apostles had abandoned their story even to protect their own families and friends, it would have been selfish compared to their ultimate earthly goal: spread Jesus' teachings to the four corners, make everyone a Christian and, possibly well after they were all gone, bring about a new age of peace and happiness. It was a gift to the whole world.
If people will give their lives for a cause, as they regularly do, then it only takes the right cause to bring them to give others' lives as well. Christianity, whether or not it was based on a real resurrection, was such a cause as the widespread martyrdom shows. Even for the long-term earthly goals alone, Christianity's founders would have thought it was worth all the horrendous sacrifice.
One more time, that's if any of this happened at all.