How good a friend are you?
If your friend is dating someone you consider to be unworthy, do you say something?
If your friend is spending too much money, drinking too much wine, or talking too much nonsense, do you call a halt?
And if your friend is a smoker, do you say: "Oh, please don't do that anymore. Not now that there are fabulous NJoy e-cigarettes which are obviously so much healthier and will make you eternally happy"?