Moral Quandary: How does the golden rule apply here?

Do unto others as you would have others do unto you. If you would want to be told then tell him. If you wouldn't care don't tell him. Seems pretty simple. It makes no sense to say if I murdered someone I wouldn't want anyone to turn me in so i won't turn anyone in. The Golden Rule does not work for harm. It umes that you would want people to do right by you so that you will do right by them. You cannot use it to countenance evil or wrong doing.