Romans 5:18 "So then as through one transgression there resulted condemnation to all men, even so through one act of righteousness there resulted justification of life to all men."

Those who deny that Genesis is an historical account of the creation of the world just denied the foundation of the gospel.  Paul's argument in the end of Romans 5 discussing original sin and because of the sin of one man, condemnation was upon all men is completely invalidated by denying a historical Genesis account.  If Adam is fictional then the Scripture fiction here too; and the basis of Christ being the second Adam, able to free all men from condemnation is gone out the window.