I think Satanism, in its modern "pop culture" context is fixated on Judeo-Christian theology because that was the dominant faith in the West, where most of this stuff originates. It is basically an act of rebellion. With the rise of secularism, people are allowed to practice and voice any idea they see fit. Satanism is primarily an adolescent phase of rebellion, although some will continue for whatever reason. It is highly illogical, because if one actually believes in Satan, then logically one actually believes in God. I find it to be more silly than threatening.