Christmas. The "holiday" based on a misunderstood and stolen story foisted upon the world in an ongoing, desperate attempt to convince the rabble that a cobbled together collection of mythological fragments makes some ancient child the Son of God and oh hey the religion (no,
not that one, and certainly
not this one) based on all that blatherskite is the correct and true faith.
My holiday has monsters.
Halloween as the night before the All Saints and All Souls day is a Christian tradition too, just like all other biggies: Christmas, Easter, Carnival, Saint Nicolas, New Year, ......
We simply have to live with the fact that our countries have a historical Christian background. It will take generations to weed those out, if ever.
Because these festivities can still be meaningfull without being a church member. People pick parts of the tradition that they like.
I love Sinterklaas en Christmas, not because of the religious aspects, but I love decorating the house, the lights in the darkness, the totally happy faces of children when they meet Sinterklaas and his Peters.
You can celebrate the festivities for Christian or pagan reasons or just for the fun of it.
Halloween and Carnival make great dress up parties without believing a thing of the Christian traditions.