I think it's safe to say that most parents use Santa as a way to manipulate their children's behavior. It's something that is deeply embedded in the Santa mythology. As declared in the famous song, "he knows if you've been bad or good, so be good for goodness sake."
It's basically Santa lore 101 - the first thing you explain to your kid is that he brings presents ONLY to the good boys and girls.
How many parents do you think have threatened their kids by saying "do you want me to call Santa and tell him not to come this year?" I'm willing to say most parents who adopt the lie have reminded their kids of Santa's little rule to get them to do what they want.
In my case, I was told that how good I was is proportional to how great the presents will be. I stressed so much over this and it made the times when I made mistakes or failed to comply so much more painful.
This Santa lie is perpetuating the control of kids. It's even easier to control kids using this lie since the idea that this magical experience might not happen is a lot more powerful than being sent to their room.
It also lets the parent dump the responsibility of being the person to emotionally harm their child, since they can say to the child, "It's not me who is threatening you of not bringing presents if you don't do what I say - it's Santa."
And forget about the immediate psychological stress that this made-up threat brings to the child. What's more harmful is the behaviorism that's involved. It's creating adults who seek external approval instead of internal, which is a recipe for an unhappy life.
This post was inspired by the latest discussion from Praxis Philosophy Nights. It was an excellent discussion with great arguments for and against the practice of lying to kids about Santa.