And, yes, I am building a strawman from your exact writings. Has little to do with what you are saying in particular. More, just getting some stuff out of my fingers. My arguments that pretend to understand what you are saying are just as caricatured as the arguments pretending to say what religious people believe.
Anyhow, I do believe in Santa Claus, but perhaps not in the form you would relate. Yes, there was most likely a Saint Nicholas, but just as the Historical Jesus, we know precious little about that person (just as there was a Buddha, and a Moses, and a Mohamed). Of these, we know more about Mohamed than any of the others. But knowing more historical information does not equate to being more or less rational (if so, the moonies would win hands down). Anyhow, I digress.
Tied up in these systems of belief, including Santa Claus and the Easter Bunny, are metaphors, symbols, myth, aspirations, etc... Indeed, at the core, the question of fact-or-fiction belies the ideas which they convey. And ideas and emotions are what are important. Indeed, the belief in rationality is a fairly recent phenomena in human history, brought on by the Renaissance and the 17th century. Ideas are what binds people together.
Santa Cluas is a shared idea - culture if you will - that seeks to teach a lesson. And what would that lesson be? I for one accept the lesson that's taught by Santa Claus, and I do so in the face of possible ridicule for believing in such absurd notions as innocence and benevolence. But then we'd just get into an argument about the commercialization of the winter solstice.