As I've said, many times, if somebody can offer me a better explanation for Christian origins than "A guy called Jesus lived a couple of thousand years ago and some people thought he was pretty cool" I would be happy to listen to it.Paul Regnier commenting at Exploring Our Matrix.
I think that Cool Jesus is a very reasonable explanation for Christian origins, and I can't claim to have a better one. Moreover, I like Cool Jesus. I like the guy who hung out with the peasants, the prostitutes and the tax-gatherers and said to them "You guys are every bit as important in God's eyes as any rich prick sitting in the front pew at the temple." I even like that Cool Jesus may have been just deluded enough to think that he had some special role in God's plan to bring about a just and righteous world. What I really like is that Cool Jesus inspired his followers to form communities in which they treated each other well enough that outsiders sat up and took notice.
I'm just not so sure that the evidence is strong enough to say that Cool Jesus wasn't invented. When I look at the earliest sources, I don't see much evidence that Paul knew anything about Cool Jesus. In the earliest sources, I only find Mystic Christ who appears to certain select individuals and reveals deep spiritual truths. Mystic Christ is the heavenly being through whom God Almighty is going to bring about His grand scheme of reconciling the world to Himself. Mystic Christ inspires admirable behavior in his followers, too, but he doesn't do it by the personal example he sets because he doesn't have much personality. It's kind of hard to relate to Mystic Christ. So maybe it's almost inevitable that someone would invent Cool Jesus just to make Mystic Christ more accessible.
The ferocity of the debate over Did Jesus Exist? seems to have surprised a lot of atheists and agnostics who didn't realize that anyone cared about the question so much. One of the most frequent comments I have seen is "Who cares? The important thing is that we all know that Magic Jesus didn't exist." However, it does seem like a lot of people care about whether Cool Jesus existed while others think that debunking Cool Jesus is just as important as debunking Magic Jesus.