Anyway, I am not sure how the anti-Da Vinci Code crowd will feel about Williams vs. Elaine Pagels, Karen King, et al, but I think this is a good point:
The various strands of belief that are labeled as Gnostic, says Mr. Williams, "were attempts at religious innovation that did not enjoy majority success. What came to be orthodox Christianity did. I treat them sociologically to understand why they were minority movements."
In other words, despite the occasional modern appeal of "Gnosticism" as something shiny and different and countercultural (and its legitimate appeal as an area of study in the field of antiquity), most ancient people found it unappealing, and they voted with their feet. This sociological approach, although not theological, is constructive in its own way. It's what Rodney Stark does in The Rise of Christianity, a successful explanation of why Christianity grew from a tiny sect of Judaism to a world religion in a relatively short span of time, without military conquest or state support for most of that period. (Stark used to be a colleague of Williams' at the UW.)
I have no problem with saying that the modern view of orthodox Christianity as "normative" came about not because The Winners Write History, but because it is obvious to most people that orthodoxy is just better. It respects the whole person, body and spirit, it treats the scriptures as a unified text and not two accounts of two radically different gods, it doesn't withold God's revelation from anyone, no matter how humble...it's just better.