How Satanism started for some..

When Christianity was introduced to the land that is known today as united kingdom, Ireland, and Scotland, pagans were forced to change their religion to Christianity, those who didn't faced a death sentence for the crimes of heresy and were burned alive...

So the oppressed pagans either changed religion, or burned alive, the ones who lived couldn't forgive the church for their crimes against them, so out of spite they read the bible, learned whose the enemy of their god so they'd worship him, so pagans came to the conclusion that Christian's hated Satan and that's when some decided to worship him...

not all deal with black magic and sacrifices as many people think, some just follow that religion to piss other people of... 

meaning stop forcing your ideologies on other people it might backfire... live and let live