"We are taught that we may disregard all obiter dicta, but, as we are never sure what the law in a given case is until some Court has given an opinion in the reports, equally are we never sure what is unnecessary law, the obiter dicta of an opinion, until some later Court so informs us. That which we have for years quoted as authority is, in later expressions, stripped of its conclusiveness and made simply an impertinence. Not only does the superfluous expression which has been cited or acted upon as decisive become indecisive, it becomes a reproach to the Judge who wrote it."