At the point where it prevents something worse from happening.
Look if you want to see everything as right or wrong, black or white, then that's your choice and you're welcome to it. I've just tried to show you that the world isn't that simple.
And no... I didn't dodge your question. I just went with your hypothetical situation to show you the possibilities that you don't seem to be able to see. I don't think you are a naive idealist. You seem somewhat rigid, conservative, and conformist. That's all fine and good but you have to learn to live with that irritation and anger you spoke of. And with that I'll leave this in Michael's capable hands. I wish you well.