and if what was advantageous at one time is now a liability
'They' is a gender neutral pronoun and like Schrodinger's cat it shows the superposition of he and she in an unknown state. Until observed, the human is simultaneously male and female.
I should read all the posts here first I suppose, but I'm a little hurried today so I just skimmed them. Just wanted to add that one thing that the "Santa Claus Cover Up" teaches our children is to give to others and not take credit for the giving personally. Through the "Santa Claus Cover Up" we teach our children altruism. When they find out that we were really Santa all along it doesn't automatically become "they lied to me" in their minds. As adults we all know that we are Santa. It is a make-believe role that we take on for our enjoyment and the enjoyment of our children. It serves as a rite of passage. Most children know in a primitive way that they have crossed a developmental threshold when they figure out the "Santa Claus Cover Up," and that they too are now Santa.
Finally the "Santa Claus Cover Up" is not just about the things we say it is about. We are all unreliable narrators of our motives and intentions because the part of our mind that does things can't use language and the part that can use language is just making stuff up. In setting up your false dilemma an option you overlooked was whether the dilemma described actually exists. Perhaps believing in Santa doesn't give children a sense of wonder, or encourage them to behave well. Then the entire quote becomes gibberish. Maybe children already have a sense of wonder and want to behave well and be rewarded for doing so. Then the "Santa Claus Cover Up" just provides them with a field to develop those talents on.