My quote is from Michael Aquino, founder of the Temple of Set, in
his reply to an anti-Satanist diatribe by Isaac Bonewits, a neo-Druid, back in 1991. Aquino wrote:
I should emphasize here that Aquino was speaking only for the Temple of Set. As far as I can tell, most Satanists would
not agree with the above as a definition of Satanism.
In any case, I don't think it's true that the idea "that the individual human consciousness is a free agent apart from the non-conscious forces of nature" has been particularly "demonized," either by Christianity or by our culture in general. Christian churches have demonized lots of things, but the above idea doesn't seem to be one of them.