Some evidence has been found recently showing that the Gospel of mark may be written fairly recently after the death of Jesus. Most skeptics sight that because the gospels were written so long after Jesus that they may have forgotten a lot of the detail and made up some things to fill in the blank spaces. But now we see that there wasn't really any time for fables to be added. I have also seen evidence for the great detail with archeological discoveries showing the exact places named and described in the new testament where the things happened in the time of Jesus. So those writings were more than likely done by 1st hand witnesses or they spoke to the witnesses. So it is hard to believe that the writers who are of sound mind from what they write would just make up blatant lies about some of the things Jesus did. I believe the things they claim happened were something the writers believed happened whether it did or not is another thing. They may have exaggerated some things but most claims are based on a truth.
We know that Jesus was Crucified for claiming to be the Son of God. So this claim would go without some other claims about Him doing some great things. Afterall the Son of a God should be able to do great things. So there would be some truth to what Jesus claimed and what others claimed He said and done. Its just whether you take the claims seriously. But then you have to begin to deny a host of prominent people who by all accounts were decent and honest people. They had reputations of being rational and wise in many cases and didn't show any evidence of being a liar or deluded in other things they spoke about and did. They were willing to die for what they believed and to many this would seem a crazy act for what would be a lie.
The recently found piece of text from the Gospel of Mark (which, for some odd reason, was found almost three years ago now and is still waiting to be published) was dated at "sometime before 90AD. That would be roughly 60 years after Jesus's supposed death...that's more than enough time for content to be added/changed/fabricated. Realistically, one year after Jesus's death would be plenty of time to change his story. Why you think otherwise is beyond my understanding.
It's interesting that you would mention the gospel of Mark and also mention the credibility of the gospels in the same breath. There's really no question that the gospel of Mark has been changed and added to over the years. Not only does it not include any mention of the virgin birth...or any birth...but it also doesn't mention any appearance of Jesus after his death. None. This link may prove informative to you...
The ?Strange? Ending of the Gospel of Mark and Why It Makes All the Difference – Biblical Archaeology Society
So, again, we know that the gospels have been altered...possibly for no other reason than creating a more interesting/inspiring story. Not only were the gospels altered...they were being altered even after they had been written! It what world do you live in if you think that people who are willing to change a story after it's been written wouldn't be willing to change it before it's been written? Sure, some of the names of people in the gospels were real people, some of the places were real places...but we also know that at least some of the events were entirely fabricated. You said this...
"So it is hard to believe that the writers who are of sound mind from what they write would just make up blatant lies about some of the things Jesus did. "
Why? Do you still believe this? Have you ever actually looked into the history of the gospels? Obviously you didn't know that at least some of the stories were entirely made up...but now that you do, do you hold the same opinion? Do you still think the accounts were gathered firsthand... or at least secondhand from witnesses? I'm hoping you realize that if that were the case, it's pretty unlikely that any of the accounts of Jesus came from anyone in those accounts. The whole problem is that you're assuming a very modern mindset was held by people 2000 years ago. The writers of the gospels didn't worry about accuracy, getting as many firsthand accounts as possible, corroborating with the other gospel writers to share sources and info...they didn't have to. People back then didn't have time to investigate the origins or validity of some obscure jewish cult...they had work to do, children to care for, lives lo live. People accepted a story or rejected it based on how popular it was, how much they liked the "message" of that story, and what kind of place they held within that story. That's all that mattered. Prophets, soothsayers, religious fanatics and the like were popping up all the time...year after year. The popular ones would develop followings... sometimes leading to dramatic changes within their parent religion...sometimes inspiring rebellion against the government...but more often than not, the power of their growing popularity would threaten those whose power was already established and they would be squashed becoming no more than a footnote in history.
As for those who were so ready to die for their religion... I'm certain that the multiple reasons why this doesn't lend any credibility to religious claims has been explained to you...and more than once. Would you like to hear them again? Or would you just accept that a willingness to die doesn't lend any credibility to religious claims?