I'm curious, what are this position's ideas on how his followers came to believe this? One common response to the general argument is that most of Jesus' disciples were martyred and would have had no motivation to die for a lie.
An important transformation is that the title of Messiah (or Christ in Greek translation) has a very specific meaning in a Jewish context, as a human king or savior of the Hebrew people. When early Christianity spread beyond Jews, this context disappeared, and the title "son of God" got reinterpreted in a Greek context, where gods could literally have children.
The Nicene Creed is one of the clearest statements of the "Jesus is God" hypothesis, but (as I said elsewhere in this thread) there are plenty of strong claims made in the gospels themselves. There are also similar claims made in many of the earlier writings of the church (if you're honestly interested, there are 10 pre-Nicene volumes at http://www.ccel.org/fathers.html .)
Not how the "witnesses" changed their beliefs and how they talked about what happened over time. Even though some of them came to distrust Joseph Smith or consider him on a wrong path, once they had convinced themselves they had seen something miraculous happen they had a hard time letting go.
They later made comments that suggested they had seen the things "in a vision" (yet most people assume an actual witnessing), the important consideration is to them it was real, and just as valid as actually seeing it. In their mind there was no difference - so they had no problem claiming they saw it first hand.
Faith is a type of insanity, so naturally you can't use the assumption of faithful people acting rationally (no motivation to die for a lie) to find truth.
As to how they came to believe it, again look at other religions, spiritual practices etc. It's quite common for followers/believers to come to believe something the leader is not saying - it has to be so, that's HOW IT WORKS.
It's similar to snake oil salespeople today like Deepak Chopra - you just make a lot of hand wavy claims about energy and quantum physics and people inject their own meaning.
Put these in a time period when education and access to information was low and et voila.