I cannot address your question fully, but I want to point out that gnosticism is not exactly as you imagine it.
Gnosis is knowledge. Very early in Christian history the term gnostic could apply to some otherwise very orthodox persons, but essentially in the sense that they were ‘well catechized’ and ‘knowledgable’ about things of the faith. Many CAF regulars would probably fall into that category today, I think some have a very sophisticated knowledge of the Christian faith.
The error we think of as gnosticism is very broad-based and variable, essentially that one can be saved by ‘special knowledge’. In other words, according to gnostics it might be said that it is what one knows (or believes) more than how one behaves and decides that ultimately saves a person.
Of course, there is a lot more to it than that, but each gnostic teacher would build upon the ideas of one or more predecessors, developing and elaborating on the teachings. So it had a tendency to morph. This is a lot like philosophy, which is elaborated with new thought from one teacher or another. One can study under different teachers and form one’s own opinion.
It is true that some gnostics did believe that what one did with his body was not ultimately important, because they saw the body as a trap for the soul, and basically evil. I think that led some people to become promiscuous.
There was a common tendency to believe that some (but not all) humans had a ‘divine spark’ inside of them, which was trapped in the mud so to say, and had to be released to be saved. If someone possessed this divine element a way could be found (with the right teacher) to release it and one could ‘return’ to become a part of God once again. I think this has Platonic elements to it.
Gnostic heretics tended to have ideas which could not be traced back to the Apostles and were very limited in distribution. Some thought that there were special trials one had to go through after death, but if the right things were said, one could get past them.
Another thing was that some factions tended to have multiple lessor gods and demi-gods. Some believed that the Old Testament god Jahweh was actually an evil god who made an evil world, and that Christ came from a hidden ‘good god’ to save us from his evil world with these special hints and clues to salvation, passed on to a select few.
This brief explanation does not do justice to the subject, I think it can be seen that the whole idea of what gnostics believed cannot be generalized in a simple few lines.
