Witches are such fun costumes aren't they? The systematic oppression of women, turning those who were free thinking, didn't conform to society, were a bit ugly, a bit odd, didn't marry ... those women being murdered and tortured in horrific ways is all just a bit of fun right?
Same with ghosts - the restless spirits of the dead are just hilarious
And vampires - drinking human blood, killing people, hunting maidens is all fun and cute!
Oo and the rotting, reanimated flesh of corpses which then feasts on the brains of the living! Zombies are adorable.
Terrifier isn't child friendly, the films are extreme to the max, but Art the Clown is now a pop culture figure like Jason, Freddie, Chucky etc. Kids will have been exposed to the character without knowing the absolute violence he comes from. Same with Squid Games - pink guards are even in Just Eat adverts!
It wasn't, however, the first "scary Santa" and it won't be the last. There's a whole series of films based on a killer Santa!
If the school has a no mask, no weapons policy then it should have been enforced
But claiming witches and zombies and vampires are somehow cuter and less horrific is ignoring their past and context the same as a child dressing as a character they only know from memes and social media rather than the film