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What you are describing is why the 1977 Additional Protocols were added.
However, if you read the preamble and Article 1 of the 2nd additional protocol, you will find:
Recalling that, in cases not covered by the law in force, the human person remains under the protection of the principles of humanity and the dictates of the public conscience,
and in Article 1,
This Protocol, which develops and supplements Article 3 common to the Geneva Conventions of 12 August 1949 without modifying its existing conditions of application, shall apply to all armed conflicts which are not covered by Article 1 of the Protocol Additional to the Geneva Conventions of 12 August 1949
Notice that first off, the statement is made that with respect to the Conventions, there is a "10th amendment" attitude to err on the side of humanity. Notice in the first article, the protocols are seen as developing the original documents. The first additional protocol supplements Article 2, the second supplements Article 1. But there is the assumption that they just develop Article 3.
The commentary from 1949 forward all indicates that there is no intention that there be situations where no protections apply. That, like I was saying, was an invention of the neocon/sovereigntist people, and it began the gradual pulling away from international humanitarian and human rights law by the U.S. for which the Reagan Revolutionaries from 1985 to the present are largely responsible.
But the reason for citing Vienna is that the U.S. has wanted to have it both ways. It wants to champion new human rights law, and even shepherd through new treaties, and wants the prestige of being considered a human rights "beacon" but then balks at ratification, or, in the case of the Rome Statute, even removes its signature so it won't face any consequences.
My personal opinion is that some of that results from a deep set belief by Reaganite Republicans that laws passed under Democrats are not required to be obeyed somehow, or should be circumvented. Long history with that, from a dual mindset on domestic social laws (Prop 8 is settled law the minute it passes, Roe v. Wade is not, no matter how long it's been in effect), to international treaties. There is also a mindset, most succinctly expressed by George W. Bush when he says "The U.S. does not torture", that the U.S. is a beacon of human rights by birthright and definition, rather than by behavior.
Vienna makes it clear what should be done if the U.S. does not want to obey the additional protocols: It should denounce them, and then wait it's one year (1st protocol) or six months (2nd protocol) to be out. But then it has to state its renunciation of humanitarianism, as they say, "In front of god and everybody". The hypocrisy of wanting the mantle without the behavior is very clear. And the racism involved with not ratifying them is very clear, too. Maybe our first post-racial president can get them ratified and end these shenanigans once and for all.