When I was Christian.......

I was always taught that the story of Adam and Eve was metaphorical and not literal creation as biologically speaking it would be impossible for 2 people have enough offspring to populate the world. Other than that I was always confused as to why Christians still credit "The Fall" as the source of all the bad things we see. ? How can metaphorical people (Adam and Eve) be responsible for a literal spiritual fall? It seems as though God created is with the intention of cursing us eventually. How are non exist people the cause for all the harm we see?