"According to one Gnostic view women were wholly creations of the Devil, as were men from the waist down*"
Rose, you need to remember that Gnosticism had been in existence for years before the birth of Christianity (they exist in Hindusim and Buddhism), so Gnostic ideas like this aren't 'Christian' ideas. As does happen in many areas of life, Gnostic ideas began to infiltrate the church, and it is generally thought that John's Gospel was written to counter a number of ideas - such as Gnostic ones - that contradicted Christian thought.
As for the passage about 'making themselves eunuchs for the kingdom of heaven's sake', the Greek has a meaning closer to " ... and there are those who choose to live like eunuchs for the sake of the kingdom of heaven." (NIV). In other words, they choose to remain celibate, arguing that if they are to serve the kingdom of heaven, (or even an employer) they can do so more efficiently by choosing to abstain from sexual activity.