We say that nobody is perfect, and that applies to us, right? Okay. Good. What about others? Do they have to be perfect, unlike us? Are they held to a higher standard by the Lord than we are, are we better than they, or is our perception of equality severely skewed?
I'm by no means saying that we shouldn't fight sin in the name of Jesus by the power of the Holy Spirit, and that we should try to encourage others to do the same, and be there with them when their sin doesn't cause us to sin ourselves. That would be a lie, and one of the worst. I'm saying that we ought to closely watch our reactions to others who are in sin confessing theirs to us in confidence, and let that be a check against our own.
You have to be sincere about what your truth is before you can sincerely change your own to the one that is truly... well, you get the point.