Ever know anyone who says something that hurts someone else's feelings and then justifies it by saying "Well, it was the truth!"; Or maybe they talk about how "the truth" sets you free; Or maybe use the old, "the truth will stand when the world's on fire" southern saying?
The Bible teaches us to "speak the truth in love". Just because something is true doesn't mean you have to say it! If it is hurtful, or demeaning or debasing, keep it to yourself! Paul talks about "whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable--if anything is excellent or praiseworthy" as being what we should be thinking and saying. If it isn't constructive and edifying, don't let it out of your mouth!
Christians don't have the luxury of opening their mouths and speaking whatever is on their minds! The Bible says that "a fool speaks his whole mind". Some people say "I just say whatever is on my mind!". The Bible says those folks are foolish!
We are supposed to speak the truth, but only in a loving, gentle and constructive way. Anything more is sinful.