They’re obsessed with satanism, similar to how some of them are obsessed with communism, because it makes their mental landscape easier to deal with. In a chaotic world where they feel they have less and less power, it’s comforting for them to think there’s some sort of order behind it, even if it’s a conspiracy by people they don’t like to change things they do like. Plus it gives them something to point to when stuff they don’t like happens. “Why do bad things happen? Those damn satanist/communists. And if we stop them, we can stop the bad things happening.” That’s way easier for someone to swallow than uncontrolled, unorganized bad things just happening in the world. So they find satanism/communism and “proof” it’s there with symbolism in things they don’t like or are scared of.