I've long entertained a dubious regard for the practice of lying to children about the existence of Santa Claus. Parents might claim that it serves to make children's lives more magical and exciting, but as a general rule, children are adequately equipped to create fantasies of their own without their parents' intervention. The two reasons I suspect rest at the bottom line are adherence to tradition, and finding it cute to see one's children believing ridiculous things.
Personally, I considered this to be a rather indecent way to treat one's own children, and have sometimes wondered whether a large proportion of conspiracy theorists owe their origins to the realization that practically all the adults in the country really are conspiring to deceive children for no tangible benefit. However, since I began frequenting this site, I've been exposed to the alternate viewpoint that this realization may be good for developing rationalists, because it provides children with the experience of discovering that they hold beliefs which are wrong and absurd, and that they must reject them.
So, how did the Santa deception affect you personally? How do you think your life might have been different without it? If your parents didn't do it to you, what are your impressions on the experience of not being lied to when most other children are?
Also, I promise to upvote anyone who links to an easy to register for community of conspiracy theorists where they would not be averse to being asked the same question.
I figured out the non-existence of Santa Claus when I was about 5, I don't remember how. Someone posing as Santa visited a relative's Christmas party I was at and gave the children gifts and the local news in my city tracks "Santa's current location" on the weather radar periodically on Christmas Eve, which kind of made it a pink goo moment for me. I was angry and confused, but mostly kept this to myself. From this experience I concluded that my parents were not completely reliable and that society has a significant disrespect for children, although I did not make much use of this information until years later. I summary of my thoughts on child deception can be found here.
I'm inclined to think that lying to children is dominance behavior-- the people who do it are reassuring themselves that they're in charge. However, it's hard to get evidence about covert motives.