As common as this this argument is, it fails at every level.
1. We don't know if the disciples were actually martyred. The evidence for this is skimpy and grossly unreliable. Much of it derives from the book of Acts which in itself has some serious problems. For instance, Acts talks about some amazing miracles performed by the disciples. And yet there's no independent mention (anywhere in contemporaneous literature) of any of these wonders. One would expect that, if Paul really did bring the young man (Acts 20:9) back to life after killing him with his boring sermon (perfect plot for a Monty Python movie, only written 2000 years ago!), somebody else would have noticed it. There would at least exist an independently attested legend. And yet, nothing. Acts is a work of theology and not of history.
2. But let's assume that many of the disciples were indeed martyred and did indeed happily go to their death. Does this mean the resurrection is true? No. Here's why.
2a. The disciples may have honestly believed in the resurrection (whether bodily or just spiritual), even if the resurrection did not in fact take place.
2a(i) they may have been mistaken. For example, if in fact there was an empty tomb (for whatever reason; and many are possible; each theory itself more likely than a resurrection) they may have wrongly but honestly concluded that Jesus was resurrected. Remember that this is the 1st century we are talking about, when superstition was on the daily menu. Also remember that the disciples were naturally traumatised by the sudden and tragic death of Jesus. Severe trauma can easily affect one's rational thought. Thirdly, if they truly believed Jesus was the messiah, it would be difficult for them to accept that he was executed and that was it. Messiah isn't supposed to die a convicts's death. Combine that with an empty tomb and you have a pretty good start to an honest and yet mistaken belief. Some or many of them may also have believed that Jesus appeared to them in some way or another. They were sure to have dreams about him. They may also have "seen" Jesus in other people (tradition of that can be seen on Luke 24; on the road to Emmaus).
2a(ii) they may have been deceived. It's possible that resurrection was a pious lie. If so, it may have been initiated by some disciples and told to the others. For instance, suppose that Peter makes up (whether consciously or by way of delusion) that he saw Jesus alive and convinces the others that this is the case. Again, we have to remember that we are talking 1st century, when superstition ruled the day. We are also talking about disciples who were simple, uneducated people. History shows us thousands of scenarios where groups of people fall for all sorts of claims propagated by a (often charismatic) single individual, or a small group. How many Mormons are there? What about Muslims? What about Charles Manson and his crew? The Wacco wackos? And thousands more.
And if some of the disciples were duped by others to believe in the resurrection, there's no reason why they couldn't happily go to death with this false belief.
But if that be the case, what of those who invented the lie? Surely they didn't have an honest belief in the resurrection. Why would they be prepared to die? Actually, they MAY have had an honest belief. Quite simply, one, two or more of the disciples may have been delusional. Delusions are a common feature of the human condition. Just ask any psychiatrist. And very often, delusional individuals have a strong religious backdrop to their delusions. Hospitals are full of people who think they are Jesus reincarnated. They're also full of people who believe they're spoken to by saints.
2b. Could the disciples (or at least some of them) deliberately lie and yet be willing to die? I left this possibility for last because this is usually how apologists put their case. "Who would be willing to die for a lie?"
The only conclusion from this is that these apologists are either childishly naive or simply dishonest. The disciples were following Jesus during his lifetime and would have continued to follow him even if he had not been crucified. They had faith in his message which in itself didn't require a resurrection. The message was na apocalyptic one. The day of judgment is near. Jesus is a king but his kingdom is not of this world. Flesh and blood can never inherit the kingdom of God. We must love one another. Whoever wants to save his life must lose it. Jesus's death on the cross did not diminish this message. Since his kingdom is not of this world, the disciples could be assured that there is a world in which Jesus reigns, with or without there being a resurrection and certainly without the need for a PHYSICAL resurrection.
The disciples weren't martyred because of resurrection. They were martyred because they followed Jesus. At the same time if they wanted their religion to spread and be successful, there's no reason why they wouldn't embellish or even invent some things. And nobody can claim that such a momentous thing as a resurrection wouldn't sound like an appealing sales pitch.
Anyone who thinks true believers can't ever invent or embellish claims should read some apocryphal gospels. For instance the gospel of St Peter (which nobody believes was written by St Peter) describes the resurrection, complete with a talking cross and Christ's head stretching up all the way to heaven. As another example, Papias, an early church father (often relied on by apologists for his claims of gospel connection to eyewitnesses), wrote about Judas Iscariot urinating worms and his body being bloated to the size of a chariot. Ridiculous stories that nobody believes. And yet, there's no doubt that both have been created by people who truly believed in Jesus.
Inventing a story or adding to an existing story or exaggerating facts in no way means that the individual doesn't truly believe OTHER facts about his religion. People exaggerate things and make up stories, often despite the best of their own intentions. It's human nature.
Would the disciples be ready to die for a lie? Probably not (though not necessarily; there's no telling they were all rational or mentally well). But would they be willing to lie in order to bolster the religion they were already prepared to die for? There's no reason whatsoever to say that they wouldn't.
To sum it all up, the apologist argument fails. The disciples' willingness to die for their beliefs doesn't mean the beliefs were based on actual facts. But even more than that. It's entirely possible that some or all of them could lie about the resurrection and yet still be ready to die for other beliefs that they did hold.
Unless Christian apologists start coming up with some convincing arguments, Christianity is going down (and we already see a trend of this in the educated world). You simply can't treat 21sf century people like idiots; we are not the gullible superstitious peasants of 1st century Middle East.
Comments are welcome.