Santa, Easter Bunny, Tooth Fairy-believed in them because they were presented as real things by my family. Fortunately, my parents didn't elaborate much or try to convince me once I became disillusioned with those notions. Not sure how or when I realized these were fake creatures, though.
Image of Santa Claus has always (and still does) make me quite uncomfortable-can't stand facial hair, so SC was scary (fat old man in creepy outfit is NOT a type of person I gravitate towards) rather than appealing. Holiday music, the whole celebratory (not celebrity) culture repels me.
Personally think it's not nice to lie to kids (just MY opinion) and make up these stories yet insist these are real-it hobbles parental credibility. Don't see any good reason to be dishonest about such a thing, other than "tradition"-which doesn't hold weight (importance) for me. Liked fairy tales & myths as a kid, but there was no confusion about the (lack of) "truth" to them.
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*"I don't know what it is, but I know what it isn't."*