The word natural has a number of definitions, but there are two that are most relevant to the debate here.
One definition refers to those parts of the universe not affected or influenced by humans. In this definition, natural and artificial are opposites.
The other definition is more science-related. In this definition everything in the universe is natural, including humans, and the supernatural encompasses everything else.
You can argue that during a discussion one should not switch back and forth between these two definitions, but one cannot argue that one definition is wrong and the other right. They are both accepted definitions.
--Percy