Your sense of justice, my friend, is your ego, don't pull it on others..or... Ordinary paradoxes of life

I know someone who' s very important part of life is changed because of someones decision to change it. And I think it's a wrong decision.. It is hurting not only that person, who's life has been changed, but even those who surround him.. But in conversation with the person who's life has been changed against he's will, he's asking me to not to interfere, even after he's agreeing with me about wrights and wrongs in this case.
It is difficult to accept injustice, even knowing that each of us have our own understanding about it.. Consequently, loyalty has its limits, cause seeing that the man is wrong in he's decisions and acitons, you have to respect his choice, even if you see him hurting someone, even if only mentally. You have to keep quiet and respect his choice, because that is what you'd like to get - non-intervention. And it is not easy to make decisions that applies to someone, especially if that decision affects his life. It's like you'd hold someones life in you hands, or very important part of it and you should decide if and what to do with it. More or less we all have someones life depending on our decisions.. I guess the question is whether we have the right to decide objectively and reasonably interfere with any life at all? Because even though we like to think that we are doing it on he's own behalf, it still remains the selfish thing. Who do we think we are to decide what is a good thing for someone, what's not. Such a decision shows a very high level of confidence and even arrogance of the decider himself..
At the same time, deliberately or not, we all are more or less distorting each other's lives. The questin is, where is the line?
So Basically we are all determined by our own internal morality, an understanding of borders, the experience, knowledge and breadth of thinking ..
And lives are affected or not.. in our own joint action, causes and consequences...
And my sense of justice turns out to be an egoism too..
Oh how useless is this dificulty to accept injustice..
How useless is my empathy.. it inspires me and leaves me with no power..