Most people seem to think the Golden Rule is all we need: "Do unto others as you would have them do unto you." Well, that would certainly be an improvement upon the more prevalent, "Do unto others before they do unto you," but it doesn't really help unless we exercise some subtlety and foresight. It is probably a good thing to tell someone if they are behaving like an ass. On the other hand, how keen are you to be the recipient of such honesty when it's the truth? Hmmm...
There's also the problem of misapprehending other people's intent -- not to mention your own! The most common cause of animosity is attribution of evil intent to someone who believes s/he is trying to do the right thing.
I propose a "Platinum Rule" that should be exercised even more assiduously than the Golden Rule. It goes like this:
"Try to understand why others think and act as they do."
Most people are sincerely trying to do what they perceive as the right thing. If you can understand why they believe that, then you have a better foundation for constructive dialogue than if you accuse them of intentional evil.
Of course, intentional evil does occur; but even then it is easier to expose if you try to explore other explanations. Nothing annoys a true evil-doer like a pointed question that assumes their innocence.
Note that I am not espousing "radical cultural relativism" -- just because you understand why someone thinks and acts as they do does not mean you agree with or excuse their behaviour; it just gives you some purchase in your attempts to talk them out of it.