This would be like saying "All Presbyterians are bad guys."
Or "All Wiccans are bad guys." (Since there seems to be some manner of link between Presbyterians and Wiccans that is rather spoopy these days).
The truth is usually that the good outnumber the bad. Among any group where the leadership becomes corrupted or coopted into evil, there will be subunits or factions which form in opposition to this leadership or control.
Even among people who would call themselves satanists - they do so as a rejection of what they see as an overly authoritarian Church structure and deity following the same notion. Is God really a capricious autocratic figure? I doubt it, and argue with similar types who assert such views are Christian. So, I understand where a few "satanists" come from. Some may go a bit farther and embrace a utilitarian idea regarding the smart/strong's right to do as they will with 'lesser' people - but even then, we can see where some would agree with another person resorting to slavery/abuse/sacrifice and others would reject such treatment and fight against those who resort to it.
People may be pigs in human clothing, so to speak, and easily steered by evil - but outright evil must put a lot of effort into deceiving good to fight against good in order for it to prevail.