I still seem happy enough to celebrate Christmas, though!
Christmas isn’t really a Christian festival – it’s the pagan midwinter festival that the Christians just hijacked and renamed. All the fun parts of Christmas – Feasting, presents, decorations, singing predate the boring Christian stuff. Same with Easter – it’s the pagan Spring festival celebrating new life – hence Easter bunnies, eggs, chicks, etc.
So you’re really celebrating pagan festivals not Christian ones.