If so, wouldn't the negative be obvious & not require stating?
As in all things, there are facets and caveats. I think your suggestion that a positive claim needs to exist before a negative claim can be made is true. At least in those cases I have given any thought.
Caveat to stating the negative: If the positive claim is idiotic, and/or detrimental to or tends toward harm to society, nature, and/or well-being of the individual or groups of individuals, the negative claim must be made as often and as forcefully as needed to eliminate or at least ameliorate the effects of the claim in the positive. We are, in essence, an example of this.