Universal sin is, perhaps, the fundamental building block of the Christian Religion. Without sin, there is no need for the atonement of Jesus, the central focus of both Mormons and Evangelicals.
C.S. Lewis, in accord with other heavy hitters of Christian apologetics, contend that the most incontrovertible tenant of Christianity is original sin. (However, my favorite exposition of this doctrine is, of course, found here.) Indeed, most all people have an internal moral compass, a conscience, that tells them that they fall short of perfection. Those people incapable of feeling guilt are considered the most dangerous and potentially monstrous of all humans. While I am not convinced that universal sin is “proven” by the facts, it is clear that most of the people we call good or conscientious would agree that falling short of internal and external aspirations is a common part of life. Falling short is part of life not simply because we are defective, it seems to be an ingrained part of being a human to recognize that we do not live up to what our consciences aspire to. Even those that are often completely blind to their own faults can usually point out the faults of others. This brings guilt, perhaps one of the most important defenses against barbarism, yet it also one of those things that invariably saps happiness and joy from life.
What Christianity brings to the table is forgiveness. Evangelists tells us: “In Christ you will be saved and forgiven, white as snow.” Where Evangelicalism and Mormonism diverge is how they dish up the meaty meal of forgiveness to the believer. (To be specific: I am talking about how the forgiveness of is felt and experienced, not about whether or not either approach is justified by scripture, revelation or theology.)