Gave their lives for a lie?

One of the main arguments that Christians use to "prove" that the Bible, and more specifically Jesus as God, is true is that the Disciples were martyred and wouldn't have given up their lives if the story of Jesus wasn't true. "People don't give up their lives based on a lie," they say. I have a friend who is a Catholic priest and this was his first cited reason for why he believed that the events in the New Testament were true.

Now, aside from the fact that we don't have proof that all of the disciples even existed and that fictional characters dying for an idea doesn't prove anything, the underlying contention that people don't give up their lives for a lie is ridiculous. People of different faiths and causes give up their lives all the time. There are martyrs for every religion and certainly they can't all be right. Christians contradict themselves when they make this argument while recognizing that Muslims sacrifice their lives quite often.

So, to provide a few examples, the following groups are full of individuals who gave their lives through suicide or martyrdom for what was an obvious lie:

Branch Davidians
The People's Temple
Order of the Solar Temple
Nazis
9/11 Hijackers
Jehova's Witnesses
Heaven's Gate Cult

In fact, there are even atheists who gave up their lives for their non-belief.  Kazimierz Łyszczyński.  The fact that this guy was killed is irrelevant to whether or not he was right.

It should be self-evident. The willingness of a person to sacrifice his life for his beliefs is not evidence of the truth of those beliefs.