RWC
The Gospel writers died for what they knew to be the truth because they witnessed it or were taught by those who did ( in Mark's case). If they knew it was a lie that they had made up would they have gone to their deaths? The facts are that they became outcasts in their own culture for preaching what they did and ultimately were put to death for it. You are incorrect when you claim that there is no proof that they died as martyers. The proof that they did is unquestionable.
You are wrong. There is no evidence whatsoever that any NT author apart from Paul died a martyr. And Paul had never met Jesus alive; he simply claimed a supernatural revelation/vision of the resurrected Christ. Such visions are common in all sort of religions, and are easy to explain without resorting to the supernatural.
In fact, nothing indicates that any gospel author had first hand knowledge of Jesus. To us, they are anonymous, and there is no indication any of them were killed.
Many JWs died for their faith, too, and all they based it on was the normal social conditioning we find in all religions. Faith does not require any "proof", it is purely emotional. People are willing to die for their convictions all over the world, without any supporting evidence.
- Jan