The economics of Christmas is...

Christmas is a joyous and festive time, and the economics of Christmas shouldn't spoil the fun. At the same time, however, we shouldn't harbor any illusions about Christmastime consumption providing a "boost" to the economy or anything like that. Consumption reduces the stock of goods available for use in future production. While there is certainly nothing wrong with this, it is important to remember that stories of Holiday spending-induced economic growth may be misleading. (#)

Myths seem to be the rule rather than the exception when is comes to "common knowledge". Why is that?