This issue was addressed partly in Satan Speaks under the "Third Side" essay.
It seems foolish doesn't it? "Satanism" was Dr. LaVey's idea, and his chosen title for the religion he formed. Laid out for all to see in the literature, on the website, and to a lesser degree, here on the board.(I say this because it takes some digging, and deciphering to find the jewels of knowledge in a sea of bantering. At least here on the upper levels.) The second
it is catagorized as "LaVeyan" and the "better idea" is formed by the deviant group, it becomes something different. Not Satanism, but a belief structure formed of their collective thought that they mask as Satanism.
Simple things are often hardest to understand, it would seem.