Are there perhaps different schools of thought within Gnosticism? I was unaware of the type of which you wrote.
There was an ascetic and a libertine form of gnostic. The ascetic was far more common, but the libertine also popped up here and there. Some argue that Paul is dealing with a Christian form of libertine gnosticism in corinth, hence his emphasis on the importance of the body throughout the letter.
The ascetics proposed that since the flesh was evil, it is something to escape from and the desires of the flesh are to be destroyed by mortification.
The libertines proposed that the flesh is meaningless and thus what you do with the flesh is meaningless. If you want to have sex with your step-mother (1 Cor 5) that's fine, it really doesn't matter. The spirit matters. THe flesh is passing and meaningless. Thus everything is permissable (1 Cor 6:12; 10:23) and nothing is harmful.
In both cases the bodily resurrection makes no sense, because who really needs a body anyway?
That was also a recurring theme in Johnsons article. Biology is meaningless. Whereas in the scriptures, your biological body is the temple of the Lord (1 Cor 6:12-20)