The literature produced by the "other" forms of Christianity looks scant only because the members of the Apostolic Church burnt it. But these other Christians were equally prolific in their writing and instruction. We happened to get lucky with the NH and Tchacos finds, which recovers part of this other literature. From it we can tell that they were very very sophisticated theologically, and were often critical of theologies of the Apostolic Church. And we can see theologies develop within the Apostolic Church that respond to the criticisms of the other Christians. The theology of the Apostolic Church would not have become what it did without the Gnostics and other Christians (and Jews) as dialogue partners.
An interesting counter-point is provided by sociologist Rodney Stark, and I provide below a few quotes from his book Cities of God (see the side bar for more details).
Purely as a matter of faith, one is free to prefer Gnostic interpretations and to avow that they give us access to secret knowledge concerning a more authentic Christianity, as several popular authors have recently done. But one is not free to claim that the early church fathers rejected these writings for nefarious reasons. The conflicts between many of these manuscripts and the New Testament are so monumental that no thinking person could embrace both (p. 142).
Elain Pagels stresses that the Gnostic writers 'did not regard themselves as "heretics"'. Of course note. But the issue of heresy is hardly a matter of self-designation. Let us assume that these writers (including forgers) sincerely believed that they possessed the truth and that the conventional Christians had it all wrong, while the conventional Christians were equally sure that theirs was the true Christianity. Within the confines of faith, the charge of heresy can be resolved objectively only on the basis of which side more accurately transmitted the original teachings of Jesus. That decision must come down to sources (152).
Had the Gnostics prevailed, they presumably would be viewed today rather more in the manner that Pagels and other 'Ivy League' Gnostics would wish, assuming that such a thing as Christianity still existed. But the Gnostics did not prevail, because they did not present nearly so plausible a faith, nor did they seem to understand how to crate sturdy organizations. Instead, most of them did and taught their own 'thing'. To sum up, the Gnostics gospels were rejected for good reason: they constitute idiosyncratic, often lurid personal visions reported by scholarly mystics, ambitious pretenders, and various outsiders who found their life's calling in dissent. Whatever else might be said about them, surely they were heretics. As N.T. Wright put it, they 'represent ... a form of spirituality which, while still claiming the name of Jesus, has left behind th every things that made Jesus who he was, and that made the early Christians what they were' (p. 154).
1. I like the word "nefarious" and I intend to use it more in daily conversation.