One duality I think of a lot is being both honest and non-critical. Now I know that many think that criticism can be kind. Tell someone everything that is wrong with them (in your opinion), and then they will become a better person, right? Well that has not been my experience. Most people don't really change because of criticism. Criticism just makes people resentful and defensive.
So what do you do when someone really does something that not just annoys you, but that you believe is really detrimental to their life. How can you not point it out? How can you not try to save them from themselves? Perhaps they are always negative. Perhaps they smoke. Perhaps they don't treat their children respectfully.
First, remember that you are not perfect and have problems too. They probably look at you and think that there are a host of things that they need to correct you on. This thought should breed empathy.
Second, evaluate the relationship. Is this person an acquaintance or even someone who may not like you? Is this person someone you don't really like? Perhaps the kindest thing you can do is to limit your interactions with the person. If your choices don't mesh, and you are very different people, separation not criticism is probably the answer.
Next, learn the art of modeling and planting seeds. If someone is always negative, model positivity. If someone talks down their children, talk as equals with your own children (and with theirs too!) Talk about the good things in your life that have been the results of your choices. Are you happier? Is your family life for the most part good? Do your kids make good choices? Are you healthy? If they complain, you can advise but watch for their response and temper your comments appropriatelly.
What if they ask for advice? Well all of us know people who do not really mean it when they ask for advice on something. They really just want to someone to listen. Know your audience and provide advice only to the extent that they want to take it. Those who are close to you may want more extensive help than those on the fringes of your life.
Is it dishonest to not point out the errors of others' ways? To not provide as much help and advice as possible when requested? No! You can remain honest and true to yourself while keeping a nonjudgmental attitude. Know when to leave. Know when to remain silent. Cultivate the ability to change the subject and to know when and how to plant seeds of truth, leaving them to germinate when the time is right.
Forget criticism as a kindness. Remember how you have felt when you have been criticized, and when you can't be honest, be quiet. Listen. You might learn something! I have always believed that if you can't say something nice, you shouldn't say anything at all!