The Evolution of a Holiday: From Executing a Priest to Being Terrified of Sex
Obviously, no one sends a greeting card to honor the martyrdom of some dude who was interrogated (and likely tortured - it was Rome and he was a Christian priest) and killed (probably in some really grotesque and humiliating fashion - again, Rome). I'm not sure it would do to have children in elementary schools cutting out construction paper implements of torture or crayon drawings of a cat being stoned to death.
America has always sold itself like a potluck dinner—“Bring your culture! Bring your grandma’s recipes! Bring the funky spices we can pretend we invented!”