> The “leave it to states” argument is inconsistent with the moral argument against “baby killing,”
This is the nirvana fallacy. If you think something is evil enough to ban, ideally you'd ban it everywhere, but if you can't do that for some reason, it's better to ban it in some places and allow it in others than it is to give up and allow it everywhere.
> The right to be free from slavery is probably the most extreme example of a fundamental right not explicit in the Constitution being read into it, but it isn’t the only one.
There's no implicit right to own slaves, since it would contradict the implicit right to not be a slave. Similarly, there's no right to kill, since it would contradict the right to not be killed.