If sin is nonsense, then the notion of a Savior from sin is absurd. There is nothing from which to be saved. But the key arguments for relativism are fatally flawed. Relativists often argue that a society that honors free speech and freedom of religion must relinquish any notion of absolute truth or morality because this stifles the free exchange of ideas. Dogmatism and moralism are unwelcome in the pluralistic public square.
Relativism is seen as required for a democracy of ideas and norms.
But this is flatly false. One may believe there are moral absolutes and also believe that the best way to reach ethical conclusions is through open discussion, dialogue, and debate. Freedom of religion and speech does not necessitate that there can be no objectively true religion or morality. I can try to persuade you of the truth of my convictions without using coercion. The relativist has abandoned the very concept of objective moral truth.