The term "legal" is most often miscarried when it has not been put in the light of a moral origin. This relationship is the first puzzle of humanity. Morals are abstract and difficult to pin down. Artificial laws (legislation) are more or less successful attempts to make instances of moral behavior concrete. I make a distinction between "artificial" and "natural" law. Morals and natural laws co-exist. Workable morals arise from natural law. For example, when A kills B, B no longer participates. There is no natural law for deciding who "should" participate. There is only natural law for determining who, what, where, when, and how. Therefore, no person can, by artifice, determine who "should" kill whom.
-- Kilgore Forelle