Most people don't understand the Satan character or what Satanism is for what seem to be a few reasons:
a.) They go by what is socially displayed as images and representations of Satan and believe that they can make Satan out to be 'whatever they want Satan to be,' that Satanism is a 'do whatever you want' religious view/philosophy, and that the ideas of "sinning" or hedonism, self-aggrandizement, and the beastial nature of humankind is somehow represented by Satan, Satan being far removed from the religious identity and that is far from correct.
b.) Think that the Bible doesn't matter concerning what defines Satan and Satan's role in both history and religion. Abrahamic religion makes it clear about the particular role that Satan plays, and though the word Satan is said to mean 'opposer' as a word with Hebrew origins, nearly every commonly accepted idea of what exactly Satan is opposing is only partially correct, if it is correct at all. Satan, as a role, is not in opposition to Christianity, or to their God; especially in Christianity and Islam, the 'opposer' is both an essential part of their relgious identity, but also an essential part to the structure of their religions themselves and this 'opposer' character is both necessary for them to achieve the goals they have outlined in their religion and necessary for the perpetuation of their religion. All three Abrahamic religions, (Judaism, Christianity, and Islam), are connected in numerous ways, but an essential connection is that of Satan and how it ties back to Judaism as a religion and its purpose.
c.) People, because the general misinformation spread as a scheme to maintain ignorance of people concerning these characters, and spread as the spread of ignorance itself due to a lack of understanding of their own religious texts, accidentally contribute to the religions to which they oppose, both by believing in Satan as a character to oppose, which is detrimental to the rest of humanity, and by Satanists, who perpetuate the religions by contributing themselves to the cause of that opposition. Their goal is to eradicate Satan, as a character, when they don't understand what the word Satan means in its application. LaVey was accurate in his assessment of Satan and what he constructed from it, but he was most accurate in his understanding that Satan is not a real character, but a label applied, with a fundamental aspect of Satanism being the acceptance of that label instead of opposing its use as a label for 'that' side of humanity. The idea of Satan being this representation of evil, the source of all things bad, the thing that is to blame for the side of humanity is purposefully propaganized and has been used since Abrahamic religion's inception, as a disinformation scheme to keep people believing the wrong thing while getting them to believe the thing that is most beneficial to the existence of their religion, that is, that Satan is a real entity and character, when Satan is not. Like I said, Satan is essential to their existence, and the belief in their particular form of dualism is more detrimental than anything.
One thing they don't understand is that the Satan character, in terms of the concepts of Hell, what Satan supposedly believes, Satan's lack of belief in a God, or in some way attempting to take over the ranks that the religions outline is incorrect, and there is also too much equivocation of characters, such as Lucifer and Satan, Belial and Satan, (and this is evident in some types of Metal), when they are not. Lucifer and Satan are not the same thing. Belial, for example, is a label which means 'worthless' or 'useless,' a description believers apply, and is of the same use as the word 'Christ' to mean 'annointed' or 'the annointed one,' when they apply the title Christ to the word Jesus as an admission of belief. Both are different from Satan because, while Belial and Christ are words that describe a state of being due to belief, the word Satan means opposer, which is a state of action, towards their beliefs. Lucifer, and by Lucifer I mean the morning-star, the character described in Ezekiel, is another name for Jesus because of what was written in Revelations. The history of the connection between Lucifer, Jesus, and the Greeks is a different topic, however, the fundamental mistake that many make is the equivocation of Lucifer to Satan. They are, Biblically, entirely different characters.
What is most particularly interesting about Biblical references to Satan is the connection of Satan to Peter, because a particular person in the New Testament story was directly referred to as Satan itself, which is why the upside down cross is associated with Satanism; its use as a symbol is not simply because of the misguided belief that inversion represents opposition when it does not.
Here is the quote concerning Peter, Jesus, and the labeling of Satan:
From that time Jesus began to show His disciples that He must go to Jerusalem, and suffer many things from the elders and chief priests and scribes, and be killed, and be raised up on the third day. 22Peter took Him aside and began to rebuke Him, saying, “God forbid it, Lord! This shall never happen to You.” 23But He turned and said to Peter, “Get behind Me, Satan! You are a stumbling block to Me; for you are not setting your mind on God’s interests, but man’s.”
According to Christian history, Peter was crucified upside down because it is said that Peter didn't feel worthy of being crucified in the same manner as Jesus supposedly did. The idea of "the opposer" comes most from this particular quote, because Peter opposed that the crucifixion and resurrection and 'torture,' as it were, was not going to happen, so it eventually came to represent the opposition to these particular events. This is where the fundies think that Satan puts it in peoples' minds that the crucifixion didn't happen (it didn't) and that the other events didn't happen (they didn't either), and where Satanists get the idea of opposing, and the use of the upside down cross as a result. So really, in short, along with Jesus' labeling The Devil as Satan, saying Satan entered Judas to betray, and The Book of Job, and parts in Joshua, and everything written of Satan after the Jesus story, all make it clear that Satan is not out to destroy their religion, but is an important part of it.
In other words, Satan's the most important part of Abrahamic religion. Without it, they have nothing to defeat. So actual Satanism is just as beneficial to their religions existence and their cause than the believers on the other side of it. This is why I believe it is necessary to look at the Satan character as a label and not something that actually exists as an entity into and of itself.
Consider this next time you listen to Satanic metal. I'm not a Satanist, but I still do, because, though I do not believe in any aspect of their religions, but of all the characters in their religions, I agree with what they call Satan the most, and disagree with Theistic Satanism.