Never. Quite possibly, this is the cruelest thing that you could do to someone. Particularly when you don't understand it or only know part of the truth (at best), anyway. Let people live; let people learn. (Those are not my words but well said.
So very true! People should not judge others if they only know one side of the story. no matter what the other person is to you. always know both sides before you judge and criticize The other person you know nothing about.