I think that most who objected to Iron Maiden didn’t give their music a critical listen. WWI Battlrs, Frontier Wars, Rime of the Ancient Mariner, Feast of Balshezzar, etc. etc. Iron Maiden covers a lot of ground.
People generally just hear a few words or a phrase in a song and base their impression of it on that. A good example from an artist other thannIM is Bruce Springsteen’a “Bornnin the USA”. Many people think it’s a patriotic song, but in reality it’s almost the exact opposite. It’s an anti-Vietnam War, anti-American song with the chorus being sung ironically.
In like fashion, the main “satanic” song by IM is “Number of the Beast”, which certainly sounds satanic. But in reality it was written by one of the band’s members about a nightmare he had about witnessing a satanic ritual, one that horrified him. It wasn’t meant to promote satanism at all, but rather to describe and express the horror he felt .