I think I agree... the analogy is simplistic and so isn't watertight. But even limited lunacy is still lunacy. Look at cult leaders such as David Koresh: cults grow because they appear plausible to their recruits (perhaps with some manipulation) but having seen what happened we'd still consider them fruitcakes rather than just a bit dappy. If they were raving to start with people wouldn't be taken in.

I suppose the questions to ask really are: a) are the New Testament accounts reliable and b) did they really happen? Because it's one thing to claim to be the Messiah but quite another to do things only the Messiah was capable of doing.