Most natural laws - such as the laws of physics - are understood to be metaphysically contingent. The world could have been such that these laws were different. Is that also supposed to be the case for ethics, according to natural law theorists? Is it a merely contingent fact that humans have "natural rights"? Surely the normative facts are supervenient - you couldn't have a world non-normatively identical to our own, but with different moral or other normative properties. If there are any moral laws at all, then they are metaphysically necessary ones: more like the laws of logic than those of nature.
If they were contingent, how could we tell whether we had rights or not? After all, there would be a world empirically identical to our own where we would lack rights. How could we possible know that we're not in that world? We would have all the same experiences and evidence. There doesn't seem any real difference between the worlds at all (certainly not any noticable differences), but that in one world we magically possess "natural rights", and in the other we don't. What does this difference amount to? I guess it would ground different normative facts. Perhaps it is wrong to kill people in one world but not the other. But that's ridiculous. A difference in moral properties must reflect a real difference in the world, and not in some free-floating moral "laws".
Anyway, I don't know anything about the natural law tradition, so let me ask my more informed readers: do natural law theorists tend to share these concerns, and so hold their moral laws to be metaphysically and not merely naturally (nomologically) necessary? (And if so, doesn't that make "natural law" something of a misnomer?)