"ή σαρξ ουκ ωϕελει ουδέν·" -Jesus (Jn.6:63b)
The flesh really does avail nothing.
To be sure, a psychoanalyst might have a day in paradise showing all of the divers ways in which Gnostics really did think that the flesh profited something. Irenaeus records in his first book Against Heresies not a few examples of Gnostic sects laying down all sorts of rules by which one may go to town and back with his body. Obviously the point of these libertinisms was to demonstrate a complete freedom from the flesh; to show that all of its lusts and activities were equally vain and could no longer touch on the future of the soul. The point, however, is not always the thought. I bet you the Gnostic church had a lot of horny individuals who would have taken up this doctrine and said, "Helllss Yes!!!!" It is these who loved their bodies after all.
Anyways, inasmuch as Gnostics formally recognized the incomparable truth of what Jesus said here, they were a step ahead of the church, which has always clung ferociously to a sort of natural bodily goodness, seeing in sinful flesh a likeness of the Divine.