I think Santa is a good tool for demonstrating to kids that God doesn't exist. Once you smash one myth you can smash them all 
If proving Santa doesn't exist convinces anyone that God doesn't exist, that person needs to learn a little bit of reasoning skill.
It's a false analogy, sorry. Santa and God both hold the trait of being faith-based. They also both share the trait of existing in an environment where their existences would be difficult to disprove (impossible for God, but let's just give that one to the proof). Thus the easily led would conclude that since they both share these traits, they should share a third trait, which is nonexistence. Santa doesn't exist, therefore God doesn't.
Apples and Limes are both fruits. They both have seeds. They both grow on trees. We have three traits in common already. Let's make a logical leap, since we will pretend to have never tasted a lime. So, knowing that apples and limes share the traits of being fruits, bearing seeds and growing on seeds, it follows that they should both be sweet, right?
Of course, that in itself is a ludicrously bad analogy, but you get the idea anyway.
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