One reason I believe Gnosticism predates Christianity is that, as Walter Schmithals suggests, several of the Nag Hammadi Gnostic tracts credit their revelatory content to Seth, Shem, Adam, or Melchizedek. Why not Jesus, Peter, Paul, and James? Of course, these latter worthies are fiven credit for other Gnostic texts, but why not all? If ther're all Christian in origin? Second, one must ask after the logical direction of influence: from Christianity to Gnosticism? Or from Gnosticism to Christianity? For my part, Harnack's schema seems more natural: he somewhere says that early Christianity combined three modules occurring with integrity in separate movements. The sacraments of initiation look like those of the ancient Mysteries. The depiction of Jesus as a miracle-working divine man matches the hero cults. And the notion of Jesus as the visible manifestation of a pre-existent heavenly being makes sense as a simplification of the Gnostic Redeemer myth. I recall how, once at the Jesus Seminar, Bruce Chilton made a striking analogy that applies well here. He told about a weekend visit to a friend's home. Going into the guest bathroom, he was amused to note that the several towels each bore the signature trademark of a different hotel chain: Omni, Marriot, Hilton, etc. What are the chances that representatives of these hotels had visited this bathroom and that each one borrowed a different logo for use in his own chain's towels? No, it is of course overwhelmingly more probable that his host had swiped each one of the towels from a different hotel he had visited. In the same way, we must ask whether it is not more natural to infer that Christianity derived these theological “towels” severally from Gnosticism, Apocalyptic and the Divine Man genre than that these three “parted Christianity's garments among them”.
(The Gospels Behind the Gospels, p. 122-123, my bold)
This point is very decisive for mythicism.
For the Roman crucifixion of Jesus is part and parcel of that “simplification of the Gnostic Redeemer myth”.
Not coincidentially, 1 Corinthians 2:6-8, the only passage in the Pauline corpus where the killers of Jesus are mentioned, is a Valentinian fragment, according to Arthur Droge. While it would be a Simonian fragment based on the Ascension of Isaiah, according to Roger Parvus.
At contrary, the Ascension of Isaiah would be a commentary of 1 Corinthians 2:6-8, according to Robert Price.
The strong clue to think that Droge is right contra Parvus is that 1 Cor 2:6-8 talks about 'perfects' and the term is explicitly Valentinian, even if also the Simonians assumed a division between insiders and outsiders. The second strong clue to support Droge contra Parvus is that we have evidence of a celestial crucifixion of the “superior Christ” among Valentinians, and obviously it would be impossible to think that the Archontes are not demons.
If 1 Corinthians 2:6-8 was without the Gnostic tenor, then this quote of the Bob Price's words would be a marginal secondary note, useful only to describe a specific detail of the Gospels: the pre-existence of Jesus.
But the Gnostic tenor is clearly visible behind 1 Corinthians 2:6-8, hence it has to dictate the extreme logical conclusion: the Roman crucifixion of Jesus is part and parcel of that “simplification of the Gnostic Redeemer myth”.