Christian author Michael Horton asks the pointed question, "What happens when we take Christ out of Christianity?" And he argues that to a great degree many mainline churches have already done so:
I am reminded of Saint Augustine's observation: "If you believe what you like in the gospels, and reject what you don't like, it is not the gospel you believe, but yourself."
You can read the introduction (by UMC Bishop Will Willimon) and first chapter of Horton's book here.