Right, but let's say that there was no law against murder. Does that mean it isn't wrong? No, it means that legislation has not yet been passed to determine the legality of that action.
If a law is passed that says that eating spinach is illegal, it doesn't mean that it's "wrong", it means that it is against the law to do so.
Laws are created by right and wrong, but also by special interests and trends of the time. Think about Prohibition. One can argue that drinking alcohol is still wrong, but it is no longer illegal. There is no longer a legal ramification against drinking a glass of beer. That does not mean that, to some, it is not still morally wrong.
Law can only enforce what is already on the books, not just what one person/people find to be "wrong". If that were the case, judges would have no precedent by which to set rulings, and cops would have no guidelines by which to arrest people.