I generally believe Jesus existed. Most knowledge was carried in the oral tradition - often for centuries or more. A social movement clearly happened around that time; it left a giant impact on history. While the origin story could have been fabricated entirely, ie, patched together from other legends and myths (lots of evidence of this borrowing), it's more likely that a person of some fame and influence was mythologized, pre-existing patterns magnetizing to him in retellings.
There were many rebellious young men at the time claiming to be God fighting the Jewish and Roman establishments in Israel. We know a man called Jesus was crucified, but the others who claimed they were God would also have been crucified, as that was the standard penalty. It was a known crime with a known punishment.
It's quite possible the Jesus story is some sort of averaging of these people (and executions) spanning several decades, with other mythology attached. But it's more likely, in my opinion, that one of these figures stood out as particularly wise.
Someone had to weave those words. That *even he* (if this explanation holds) was crucified in brutal prejudice would have been striking, tragic, and strikingly tragic to his followers.
I see no reason to ignore the historical setting - the fact quite a few young men matched Jesus's broad description as heretic, prophet, and leader claiming to be God or hear from God directly - and insist NO such person existed. And, again, I see little reason to believe that the words of a particularly wise and memorable individual of this kind could not have been remembered for a few decades before they were written down. Oral tradition was the norm, not the exception.
By the time the words were written, it seems there was already a movement and religion. It isn't as if the words were written, sat in a book for some time, and slowly built a following with people who appreciated the book. It's more as if a religious leader created a movement and eventually followers recorded a mixture of fact and legend.
Still, he may be a sort of Everyman character representing a couple generations of rebels and heretics, the voice of the pure Jewish spirit under Roman domination before much (not most but a lot) of the population at the capital was slaughtered (a definitely real event, not long after, that would have been symbolized well by crucifixion, an iconically Roman punishment).
Whether it's true or not, I like the idea that some actual words of one of the rebels were remembered. And I don't find that at all implausible.
All this basically is what Reza Aslan says in his book Zealot, but I find it persuasive.