He weakens their Faith in Christ having been deceived over his existence!
It would be nice if he were St Nicholas of Myra, but he isn't! He hasn't even been CRB checked!
Thousands of letters are sent to 'Lapland'. Where do they all go? An icy landfill? No Bishop of England and Wales would applaud that!
Rich children get flashy, expensive presents from him, but all poor children get is a lump of coal and a satsuma, even when they give him mince pies!
There is no mention of Father Christmas in the Sacred Tradition of the Church or the Catechism! Burn him!
See Fr Ray Blake's post and a link to the story of the Argentinian priest who scandalised a whole town by being honest about the awful truth of Father Christmas, Santa Claus, or, as we Catholics like to call him, Beelzebub in festive drag!