I know, I merely point out the minor(?) absurdity of killing creatures of the intelligence level of dolphin/porpoises deliberately vs humans. AFAIK, it's the deliberate act of snuffing out a human life with magic that brings Lawbreaker. Perhaps the implication is that all other critters (Vamps, Fae, etc) were either a byproduct of the act of creation and so are not off-limits OR are actually the result of the power of the human imagination causing them to coalesce. If the latter, then due to the early strength of human imagination, these entities wield immense power which makes them hard to put down.