Therefore you have no excuse, O man, every one of you who judges. For in passing judgment on another you condemn yourself, because you, the judge, practice the very same things.
Romans 2:1 ESV

This doesn't prohibit pointing out that something is sin. It's about being humble and recognizing that you are accountable to the same standards as everyone else and about not denigrating someone else because they are a sinner for doing the very same thing that you do. We are required to make a distinction between right and wrong and to teach others to do what's right. Just be sure that you are doing so in humility and gentleness, with the full understanding that you are guilty of sin too.