Can a person growing up today with easy access to the knowledge of today, and who nevertheless decides to believe in one or more magic sky-daddies, be classified as sane?

Based on the way your phrasing the question I don't think you want any other answer than the one you expect.

However if you can scientifically prove where the matter came from, with nothing to begin with then I might change my belief in my Sky-Daddy.

Something had to at one point come from nothing, an intelligent design or some freak accident. Which seems more plausible?

Just asking a question.
I can't even prove where the puddle I stepped in yesterday came from. Why should I start believing in pink unicorns, teapots orbiting Alpha Centauri or magic Sky-Daddies because I don't know the answer to a question?
Why do you think that something had to come from nothing? And why would this idea lead you to believe in magic Sky-Daddies?

yes, this is possible.

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Remedial English - Rule #2:

Always check your answers against Google search results.

Usually because they don't want to.

For some people religion is all they have, others are scared of death, some enjoy the community it provides, more find it an easy answer to something that is far from easy to answer, others genuinely just believe (make of that what you will). For most though it's because they were conditioned as children. It's a powerful force to counter, especially if your parents were very religious.

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Manu Chao - Bongo Bong

"Patriotism is the virtue of the vicious." - Oscar Wilde

"Nothing doth more hurt in a state than that cunning men pass for wise." - Sir Francis Bacon

Could you explain how?

I's no coincidence that 95% of people are the same religion as their parents. If you have Catholic parents, chances are you're Catholic. If you have Muslim parents, chances are you're Muslim etc....

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Manu Chao - Bongo Bong

"Patriotism is the virtue of the vicious." - Oscar Wilde

"Nothing doth more hurt in a state than that cunning men pass for wise." - Sir Francis Bacon

I can certainly understand how people who are almost adults today and who have been conditioned since childhood to believe in whatever their parents believed could have a hard time putting the brainwashing behind them.

But still, if they live in free societies with easy access to libraries and knowledge, it seems hard to understand how they would not throw off their mistake.

I can understand how that would be the case in a society where no possibility of self-education existed. But in today's free societies full of knowledge, it is hard to understand.

It's not hard, like I said, many don't want to and many can't.

I wasn't conditioned too hard but there's still a part of me that occasionally thinks, maybe. It would go If there were solid proof against the existence of God. Unfortunately there is only very compelling logical but circumstantial evidence.

Unless I missed something lol

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Manu Chao - Bongo Bong

"Patriotism is the virtue of the vicious." - Oscar Wilde

"Nothing doth more hurt in a state than that cunning men pass for wise." - Sir Francis Bacon