That always sounded like an unimaginative argument. Another possibility is that his followers exaggerated his words and deeds after his death.
There is very little objective reason to believe that to be the case. There are (themselves mostly unsubstantiated) stories that a number of the inner circle of contemporaries, some of whom are also identified as witnesses of the resurrection, died for the faith, which is both considerably less than "all of his followers", and considerably less established as objective historical fact rather than part of the same system of mythology.
It's certainly a fact that a little later, a lot of people who could not have been witnesses to the resurrection at the time it is held to have happened died for the faith (whether willing or not), but they obviously don't support the argument you are making.
You can't rest a claim that one element of myth is objective fact on the argument that other elements of the same myth -- with no more objective support -- seem more likely if the first element is true.
Well that's the right idea, though. Taking it a few steps further, what would be more likely, that the vatican is a power hungry institution like any other, or that a pope is chosen by god himself, sometimes two of opposing believe at the same time even.
I think it is highly likely that His followers believed strongly that He was the Messiah and His message had divine provenance.
It's much less clear which parts of, what became, the accepted view they considered worth dying for.
Maybe they believed in the truth of the Resurrection. Maybe they weren't aware of the claims (ok that's unlikely). Maybe they were aware and decided that it was good for the message (much more believable). Maybe they thought that it wasn't that important to the overall mission either way.
I don't know the answer, of course, but it's perfectly plausible that they didn't believe in the Resurrection and still fulfilled their mission. Plenty of people have died for what they believe is right without needing to have a mentor rise from the dead.
Everyone else died from a story making every single person on that list irrelevant.
ed: There is a very long list of people who where assumed to be dead before 'coming back' so even people who where 'there' don't mean much. It's not like someone was beheaded and the head grew back.
I appreciate the list of martyrs but it is hardly unique to Christianity.
Additionally, the great majority of Jesus' teaching depends on a context that admits unabashedly of a supreme Creator to Whom we owe, well, everything. Thus Jesus' teaching that lusting after a woman internally is tantamount to adultery only makes sense in the given Judeo-Christian context. So, even if we ignore claims of divinity and the origin of those claims, it's difficult to find a coherent moral message absent some claim regarding the existence of an ultimate Creator.