Under the concepts of the Law Of Nations, McCain was not ineligible. See section 217 Vol I of Law of Nations. That section provides that those born in the military service or diplomatic corps while the parents are outside the country but serving it, are considered "born in the country" because they never left it's jurisdiction.
Regarding Vattel, you are correct.
But, under the Naturalization Act of 1795, he was ineligible. The State Department manual states that individuals born overseas to parents in the military may not meet the Constitutional definition of natural born citizen.
Additionally, to my knowledge, no one has claimed that the United States recognizes anyone other than citizens born overseas to diplomats in service to the nation as anything other than citizens, which is right in line with the various Naturalization Acts going back to 1795. Military bases are not sovereign territory; there are court cases providing precedent to support this.
So, there are a number of problems with making the assumption that you've made. Yes, it sounds unfair, but the law is the reality and it is what it is. McCain's eligibility was on shaky ground, just as shaky as Obama's. But, McCains's got a great deal of play in the media and a very questionable Senate Resolution. Obama's got swept under the rug.
I am aware of that section but there is something about McCain’s situation that makes it not applicable. I’ll try to find that reference but perhaps someone reading wouldn’t mind helping out - Beckwith, you there?
I see someone knows - post 260. So McCain’s part in this whole farce is far from innocent.