This argument is fallacious and does not address historicity in any way. People throughout history have, in fact, died for beliefs which turned out to be false, deceptive, or poorly understood; such as suicide bombers being rewarded with virgins. Just because these men so firmly believed that their beliefs were true that they were willing to die for them does not give their beliefs any credibility. Here is an extensive list of refutations to this terrible argument.
Even this is making the generous assumption that the martyrs in question even existed. Some martyr-stories are known to be completely fabricated; the hagiography of St. Catherine of Alexandria, for example, is a partial rip-off of the story of Hypatia of Alexandria, the pagan philosopher who was skinned to death with tiles (by Christians!).
To break up the awkward silence at the start of a recent Overcoming Bias meetup, I asked everyone present to tell their rationalist origin story - a key event or fact that played a role in their first beginning to aspire to rationality. This worked surprisingly well (and I would recommend it for future meetups).
I think I've already told enough of my own origin story on Overcoming Bias: how I was digging in my parents' yard as a kid and found a tarnished silver amulet inscribed with Bayes's Theorem, and how I wore it to bed that night and dreamed of a woman in white, holding an ancient leather-bound book called Judgment Under Uncertainty: Heuristics and Biases (eds. D. Kahneman, P. Slovic, and A. Tversky, 1982)... but there's no need to go into that again.
So, seriously... how did you originally go down that road?
Added: For some odd reason, many of the commenters here seem to have had a single experience in common - namely, at some point, encountering Overcoming Bias... But I'm especially interested in what it takes to get the transition started - crossing the first divide. This would be very valuable knowledge if it can be generalized. If that did happen at OB, please try to specify what was the crucial "Aha!" insight (down to the specific post if possible).