What a puritanical prig you are!
Christmas has for centuries been a beautiful and happy celebration of the birth of Our Lord, which has inspired countless works of art and given joy to millions. It does not matter in the least that it may have co-opted the Roman Saturnalia, or other pagan European winter festivals. And who is to say that these pre-Christian festivals were "evil"? Is it "evil" to have a good time? Is it "evil" not to be aware of the gospels, before they have even been written?
As for the notion that children are psychologically damaged by the myth of Father Christmas, what pompous twaddle. By the way, there is no connection I can find between "Old Nick" as a synonym for the Devil and St Nicholas. The origin seems obscure, though I did find some speculations here:
Why is the English devil "old"?