It is easier not to get involved. And, everyone is doing it. Or we simply opt for peace at any price, and painful differences are never resolved. It was because both Nathan and Jesus took sin seriously that loving confrontation took place. To ignore flagrant sin is to concede it and indirectly to encourage it.
Sin is never private.
It always involves a breach of relationships with God, with the other person, and with the community of faith. First, go to the erring person alone and discuss the fault. This enables you to respect the needs and honor of another, rather than to embarrass him before others. If he responds affirmatively, you have gained a brother. This step also preserves confidentiality.