I'll admit right off the bat that this is a tough topic. We are called to not judge one another, yet many times in the scripture it says that believers will bear fruit. What is the balance? Where does accountability come into play?
I struggle with these questions myself. How do I honor God by not being critical, yet be a voice when someone is needing an outside perspective? We see in the Word, times when God used a person to bring another person into repentance (I think of King David and the prophet Nathan 2 Samuel 12). So how do we strike a balance in a world that says: What's good for you, is good for you and what's good for me, is good for me!
Many have a view of Christians as being loud, opinionated hypocrites. So before we begin holding others accountable, we have to be sure our lives are being lived for the Lord. Making sure we don't have one foot in the world and the other in God's kingdom. We must make sure that we are living authentic lives before God and others.
Sure we're not perfect, but we must strive towards actively keeping the plank out of our own eye (making sure in doing this pride doesn't creep in!) In keeping our lives pure and holy before God, others will see that and it will bring credit to our name and reputation (remember though it's not about us, but about glorifying God in and with our lives!)
I also believe that if you feel led to confront someone on a sin, you must have a relationship established. When you've taken the time to really get to know someone, it leans credit to being able to speak freely.
Also, remember we have allowed this mindset to creep into our churches. Many come and love the grace message, but refuse to admit we have to preach truth along side that. Christ also struck a perfect balance of grace and truth. As we grow in His likeness, we can ask Him to give us this ability to present grace and truth in a perfect balance.
How do you feel one can strike a good balance in this area?