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.
How do you want to be defined? By one action? By some opinion that could evolve? By a mistake, regrettable only with hindsight? Or by the sum of your parts? Okay, do that for other people. Start the trend.