In our Facebook group, I have frequently written about the importance of authenticity and vulnerability to create trust--even trust in yourself. If you can be vulnerable and open about yourself, then when someone chooses to love you, you can believe that they love the real you and not the mask you are wearing. It helps you to feel more safe in your relationships.
About a year ago, I heard my friend Dr. H. Wallace Goddard give a talk about honesty in relationships. He asked how we feel when someone begins a statement with the words "I'm just going to be honest with you." You immediately cringe right? You are waiting for harshness. Is it good for a relationship when you just come out and "tell it like it is." No. I agree with Wally Goddard. Sometimes discretion is the better part of valor. You don't need to pick at someone and point out all of their faults or mistakes to have an honest relationship.
Here's the thing. When I urge authenticity and vulnerability, I am suggesting that you are honest about your own fears and insecurities, and that you be open with the other person about yourself. That is far different from being open and honest with the other person about your perceptions of their flaws.
One of the biggest problems I see in relationships is the instinct to confess one another's sins. It is an instinct I should resist. Most of the divorced people in this group will relate to the situation of talking to a spouse about a concern, where the spouse feels attacked and turns the tables pointing out something wrong that you have done. From there it is a race to the bottom with both people criticizing and attacking each other and nobody really listening. Sometimes there are hard things we need to discuss in a marriage. But that will not be a productive discussion if it is conducted in a way that makes both people defensive. Think about brainstorming rather than fighting. Think about listening, really listening, and caring about how the other person feels more than about winning a point.
I encourage honesty in relationships. But the vast majority of the honesty should be about your own weaknesses and insecurities and your own "stuff." Just being honest about your partner's flaws--well, that is looking for the mote in your partner's eye when you can't see past the beam in your own eye. Once the beam is out of your own eye, how can you remove the mote from someone else's? Very gently. The analogy Jesus uses is brilliant. How would you want someone else to help remove something from your eye? Very gently with the intent to protect your safety.