This is something I've been pondering for a while and would like some outside opinions, gnostic or otherwise.
If the creator (Demiurge) is a flawed being that seeks to keep our soul/spirit/divine spark trapped on this material plane that it has created and the chosen people of this flawed, false god are the Semites, then doesn't that mean that Jews are essentally diametrically opposed from gnostics. In other words, isn't gnosticism in essance the exact opposite of Judaism.
Not in my opinion.
For starters one of the first Gnostic groups, the Sethians,
were Jewish. Having a different cosmology concerning the Hebrew deity doesn't make a person or group anti-Semitic, only if they start being violent, harassing or otherwise persecuting Jews would they be anti-semitic.
Later Gnostic groups, e.g. the Valentinians, were known (and criticised) for their tolerant and liberal views concerning other faiths - for example a person whether they were Christian, Pagan or Jew could attend and take part in a Valentinian ritual prayer and/or listen to their teachings.
Gnosticism by it's nature is highly allegorical, the Demiurge could be seen as the demonising of the Jewish God, or he could be seen as the veil of ignorance that shields the light of truth from people's eyes - as the latter he is the "God of this world" the world that blinds people. Seeing as the Gnostic traditions are all of Judaic descent, the "God of this world" becomes YHWH by default as his original covenant was all about the acquisition of land, and many of his rules involved material concerns.
Remember that for the Sethians, unlike the Valentinians, there were no Christian "God of love" texts to base their cosmology on. The God of the Jews, for them, was the distant father, the monad or bythos. The Demiurge and his clergy being the veil that prevented the average Joe on the street from realising this.