From Pelikan's first volume of The Christian Tradition:
[The Savior] is also a way of distinguishing between Gnostic and non-Gnostic species of Christianity, for one of the characteristics of Gnostic doctrine was its denial that the Savior was possessed of a material, fleshly body .... an explicit effort to protect the person of the Savior from involvement in matter and in suffering soon became a hallmark of most Christian Gnostics.
Is Docetism a necessary feature of the label "Gnosticism", and are all Gnostics necessary Docetist, or are there examples of Gnostics that were not Docetist?
If Docetism is a necessary feature of Gnostics, why is this so? Pelikan mentions that they were very concerned with preserving the conflation of the Savior with matter.