People who call themselves 'satanists' are very often not stupid people. I believe the origin of the word 'satan' is 'one who stands in opposition' or something like that. Satanists do not worship some kind of Christian deity, they don't worship anything, they simply adopt the imagery and mythology of the Christian Satan, in a somewhat ironic and tongue-in-cheek way, as an act of provocation, in order to assume a stance of opposition to belief systems that they see as hypocritical and delusional.
It's not an esoteric belief system, but is closer to a kind of radical humanism, where extreme imagery is used in a lighthearted way in order to shock and provoke.
Satanists do not 'worship' Satan, they do not believe in deities.