Isn't Little Red Riding Hood the most common fairytale kids in the Western world are nursed to sleep with? That's a story of a little girl and her grandmother being eaten by a wolf, who's then eviscerated with an axe.
And, because I'm Greek, my readings included tomes of Greek history and legends "for kids", where someone always got killed, exiled, adbucted, raped, turned to stone or transformed into an animal, an insect [2], or a tree- including of course the story of Prometheus. You know- the guy that got chained to a rock and had an eagle eating his liver every day.
I read all that as a pre-teen. As a teen I read H.P. Lovecraft and Harry Potter. Harry Potter is probably the most benign, a series full of people getting murdered left and right, in all manner of grim ways, killed by monsters, their soul sucked by evil spirits, exiled to nether dimensions and blown to bits by spells cast by evil warlocks. Lovecraft is probably too scary even for some adults.
And yet, guys, I'm alright, OK? I'm not an axe murderer, a maniac, or a psycho. I'm not violent, I'm an independent adult, I'm not a criminal, or a drug addict, or an alcoholic, or a gambler, or all manner of fucked-up things that little kids can turn to when they grow up in this cruel world.
So, what's up? Is it really the themes of violence and terror that's harmful to kids, or the way those themes are presented? I certainly would rather my kids read old Hesiod, than watch those mind-numbingly stupid "kids'" youtube videos. But, if I could survive the story of Prometheus without turning into a psycho, I think most kids should be able to outgrow Hulk and Spiderman being buried in sand to their necks.
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[1] The only thing more depressing than that book are the books by A. I. Cronin, which I got as birthday presents in my teens.
[2] Yeah, I know insects are technically animals, too (as in members of the kingdom animalia). But, come on. Not animals animals...