Excellent question. Instead of putting the onus on those of us who dislike the "fiction presented as fact to little children stories" like Santa Claus, I think it should be on those of you who feel this is an appropriate way to raise your children. What do you or your children gain by having you lie to them?
I'm not talking about protecting them from the horrors of violence or breasts or anything, you may think they aren't old enough to comprehend these things and that's your decision. But why make up false stories to explain things that you don't need to hide from them? Surely you don't think your children are so innocent and of such low intellect that they can't comprehend you are the one purchasing gifts for them?
Perhaps Santa Claus has another, even more insidious purpose. By establishing the gift of material goods as a reward for good behaviour, the children must logically assume that those children who receive more gifts were somehow better. Since it's the rich children that invariably receive more and better gifts, the whole mythos serves to re-establish the economic class system in this country. Rich people really are better than poor people, even Santa knows it! Let's just throw the poor people in prison where the belong so they won't trouble the rich white people.