Billy: I've read the Satanic Bible and from what it says Satan is used as a figurehead to represent man's animal nature. Unless I was missing something and LaVey was just saying that as some sort of misdirection (which, knowing him, could be possible) that's what they appear to believe.

Personally, I am not sure about whether or not the story makes sense about the fall. I also wonder sometimes if it's just meant to be metaphorical, like a lot of the rest of the Bible appears to be rather than something that was meant for people to believe literally.