See Richard Carrier's article on the "Christianity is true because martyrs died for the cause" gambit.
The Christian can't demonstrate that the early Christians "died for anything more than a vision, and visions are ubiquitous across religions—even now, but then especially," or that they "could have avoided their deaths by recanting. Or even that what they died for was their belief in the resurrection, rather than their moral vision for society, or (I could have added) some other belief they wouldn’t recant—such as their already-Jewish refusal to worship pagan gods, the only thing Pliny really ever killed Christians for (the resurrection was never even at issue); and that’s the only explicitly eyewitness account we have of any Christians being killed for anything in the whole first hundred years of the religion."
Also, there are lots of examples of folks dying for a lie.
