It isn't wrong to keep silent at times; as the Bible says, there is "a time to be silent and a time to speak" (Ecclesiastes 3:7). After Jesus' miraculous birth, the Bible says His mother "treasured up all these things and pondered them in her heart" (Luke 2:19).
People who speak their minds all the time not only end up offending others, but often saying things that aren't true. After all, is every thought you have about someone accurate or right? No, of course not; our opinions or judgments may be based on incomplete or false information, or even totally in error. Later on, in fact, we may find out we were completely wrong about someone. The Bible warns that only the fool "delights in airing his own opinions" (Proverbs 18:2).
Instead, the Bible instructs us to guard our tongues from speaking evil of others, and to say only what is constructive. It says, "Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen" (Ephesians 4:29).
Does that mean we never rebuke someone for their wrong behavior? No, of course not - but our motive is to help them, not tear them down. Yield your tongue - and your whole self - to Jesus Christ, and ask Him to help you be a blessing to others.