Non-Christians don't believe in sin. How can they without God? God has etched sin on everyone's heart but the more they sin, the deeper into depravity they sink.
Christians OTOH are meant to be the salt of the world. It is our responsibility to convict the world of sin, righteousness and of judgment. God will bless us in our calling when we are faithful. When we are unfaithful, God withholds His blessings.
The true barometer of how obedient we are to our calling is how we are influencing society around us. If society is sinking into depravity, it is simply because we as Christians are unfaithful to our calling.
IMHO, we as the church and body of Christ have failed miserably to act any differently than the world. We need to stand up and be counted.