What would you call someone if they believed in certain things in multiple religions but disagrees with just as much as they believe in each one?

A non-believer or a hypocrite.

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I think that, if you HAVE to classify that (which you don't), you would call that person an Agnostic. Agnostics don't adhere to any specific religion, but they don't deny the possibility of God's existence.

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I'd call the person a skeptic.

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I would say this person is trying to be factual and deciding which religious faith to believe in. Without knowledge we can't make good decisions. I'm a Christian and I've known it for many years (since I was a child) and I didn't have to search far to find out what I believe in, but I'm wise enough to know other people are looking for answers to their existence and through knowledge they will eventually make their own choices.

new answer

Honest.