Do I sin because of Adam?

[The Grand Nudger]

I'm focussed on your choice of words there. "Better" implies more suited for a job or more desirable. So you recognise the non-literal reading as better yet choose the lesser reading from the choices as recognised by yourself.

Yet what? Think about the question you just asked, and then come back with something coherent?

This is very telling, that you can identify a "better" reading, insist on the opposite, then want me to give you a "key" so that you can choose what you yourself thinks is better. While the whole time you simply had that key misplaced (or purposely hidden).
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Who's insisting upon the opposite? Not that literal is some sort of opposite for metaphor in the first place. I don't require either reading. I prefer the one I gave because I find it more entertaining, more insightful of the people who dreamt it up etc- in short it's a better story in all of the ways I judge stories. Whether or not I think the reading I offered is better isn't going to tell me anything about whether or not the folks who put it to paper believed that it was an actual event (we've clearly got some now that believe this - I'd be surprised if there weren't some then). I'd suggest, that as a religious narrative which helps to establish the relationship, authority, and story of a god - the folks who developed it and kept it alive were likely to believe it was an actual event, as stated - otherwise they'd be drawing authority for their god from metaphor - or more plainly put - fiction.

Similarly, you, as a christian, are going to require that something -somewhere - be literal. I appreciate that this narrative isn't it, this isn't the place where you feel like falling on your sword (and I don't blame you because the story is pretty ridiculous, even as metaphor, what with the dragons and all).