Testimony is Evidence

[Fake Messiah]

I'm perfectly capable of believing that the 3 billion or so Christians throughout history were ALL deluded, ALL misinterpreting their experiences, and that NONE could have got direct corroboration of observations that I would value enough to decide to accept the God idea in general, or the Christian Jesus-as-God idea in specific.

I'm also quite capable of believing this.  I sincerely believe that they were all deluded, just passing the same unsubstantiated claims down the line from generation to generation (and occasionally disagreeing enough with one another to splinter into rival sects).

Well yeah that was before the "scientific method" was invented. In the past people only valued what was written in the old books and the older the better. First person that seemed to brake this mold was actually Leonardo da Vinci. Back in early 15 century people "rediscovered" books by Roman architect Vitruvius called "De architectura" where, among other things, was described proportions of man. Many artists tried drawing what Vitruvius described and failed until Leonardo read it and understood it well.

After he drew what is now known as Vitruvian Man Leonardo also wanted to draw human anatomy as it looks inside. So his mentality then was to look into old books describing human anatomy and he came to books by famed and ancient Greek physician Galen. When Leonardo tried to draw disposition of human organs inside the body he concluded that Galen is nothing more then a quack who didn't know anything about human body, so Leonardo made a revolutionary decision to dissect human beings and draw what's inside them. That of course resulted in breathtaking drawings of human insides which changed the medicine and science in general. After him came of course Galileo who started measuring and observing world around him even more and that's why he got into trouble. Back in those days you looked ridiculous if you got your knowledge by "just" observing world around you instead of looking into books that were at least thousand years old.