Satanism is just a contrived thing, and I’m not even sure it rises to a level greater than paganism in Biblical condemnation. Far worse is the cult of Moloch, which in Biblical terms is an unpardonable offense, punishable by death, even of those who know of it but do nothing to stop it.
The Bible speaks of only two unpardonable (unforgivable) sins.
1. Blaspheming against he Holy Spirit, that is, attributing the power and work of the Holy Spirit to a demon. See Mark 3:28-30 and Matthew 12:31-32).
2. Adding to or taking away words from the book of the prophesy we call the “Revelation of Jesus Christ.” Any who do this will have no part in the true of life, that is, the eternal abode of believers, the heavenly city of new Jerusalem. See Revelation 22:18-19, 21:10.
3. Worshipping the beast and taking his mark. See Revelation 14:9-10.
One can argue that such a person is so darkened that only then would some one commits such acts. That is a rationalization. The blasphemy (speech) of (1) is called an unforgivable sin. (2) and (3) are acts with eternal consequences. All other blasphemies and acts are forgivable. This would include idolatry and murdering the innocent.