I disagree with DD's list of the different types of Satanists. Since it's only fair to count those who actually call themselves Satanists, there are only two types: the self-important "xian-haters" who just want to spite Christians, and rebellious lackwits, most (but not all) of whom are kids. The "Lord's Prayer backwards" classification can be eliminated, since both of the above groups partake in such activities. And I wouldn't really classify LaVey et al as "merry pranksters"; I think "abrasive instigators" is a more apt description. Group One does what it does superficially but loudly, hoping to attract negative attention and emotional reaction. Group Two does what it does simply because it's "not supposed to" and wants to prove to itself that it nevertheless can if it wants. Group One consists of people who are absolutely no threat because they have no compelling need to do anything truly bizarre; merely irritating people is enough for them. People who invent idiotic/cruel "rituals", sacrifice kittens, and knock over gravestones belong to Group Two. People who are called "Satanists" by other groups don't count if they don't declare themselves to be so; people who belong to the Temple of Set (for example) don't call themselves Satanist; therefore, they are not.
When a member of one of these groups (practically guaranteed to be exclusively Group Two) damages property or life, they should be prosecuted. Otherwise, none of these people should be taken seriously. Group One can be easily ignored, and nearly everybody in Group Two will eventually grow up and get a life. Meanwhile, we have these people to thank (albeit indirectly) for messes like the SRA scare of the 80s.