... My argument is against an externalized god. Satanism is a better argument against theism than atheism is...
Just a tiny technical detail: Satanism is not an argument against theism, it *is* theism. What's cuter still is the common variants are little more than Christian striation cults. From simplistic inversions of Christian teachings and symbols (Good->Evil, Cross->Upside-down Cross) to sublime interpretations of Sufis*, who worship Satan as the greatest lover of God -- like Christ, receiving the ultimate punishment for embodying the ultimate truth**.
*Islam, at least for the nonbelievers: Judaism +1 prophet = Christianity, +another prophet = Islam.
**The punishment, of course, is not defeat, but being cast away from the one he adored (God). As he fell to the depths of hell, a feather parted from his wing. As it fell to earth, it became Satan's first gift to man: Freedom.
Satanism, as with any number of ideologies, is a tangled wreck of intersecting themes, ideas, practices and interpretations.
My satanism redefines deity into something so radically mundane as to render sacredness itself common. Of course, I maintain that this redefinition is needed for any valid discussion of god to be more than a creepy, overmedicated set of empty quotes and salesmanship of snipehunting gear.