The Pledge, on the other hand, pledges the population to a nongovernmental abstraction - the flag - which is neither a government, nor a constitution, nor a god
In response, one "Dan" replied, in part:
No, it doesn't. You pledge allegiance to the flag of the USA, "and to the Republic for which it stands, one nation, under God" (emphasis mine). The Pledge of allegiance is a pledge to a specific flag, and to a specific government represented by that flag, which is under a specific god. There's nothing the slightest bit abstract about it.
I don't recognize that "the Republic for which it stands" is a government. For one thing, "the Republic" is itself an abstraction. The government of the United States isn't referred to in American English as "the Republic". Some conservative types like to refer to "the Republic" when they're talking about an ideal from which the actual United States is, they feel, diverging. Of course, many of those conservative types are reprehensable tools like Pat Buchanan, but my rhetorical point still stands: abstraction. Not the government, but the ideal. Not "Senatus Populusque Romanus", but "Res Publica Romana".
Now that I've thought about it, I believe that the "under God" insertion helps prevent the religiously literal-minded from construing the Pledge as a ritual worshipping a tutelary deity in the form of a flag - a literal graven image. Speaking as a hard agnostic, I'm willing to trade the complaints of fellow agnostics and atheists for compromise with the literal-minded religious.
As for "specific god", you can't get more ecumenical than the God of the pledge. He/she/it has no characteristics but a grammatical masculinity which cannot be exchanged in English for a more neutral gender - "god" serving as both neuter and masculine. It's not Adonai, or Jehovah, or YHWH, or the Lord, or Jesus Christ, or Allah, or whatever silly skiffy construct it is that Scientologists worship when they're funneling their sucker-cash to the Church.
Squint hard enough, and that "God" looks like the first-principle, the sparking impulse which even the hardest atheist has to acknowledge, and still admit that the universe had a beginning, and thus, an existence outside of the perceptions of the self.
Well, I can think of a few breeds of agnostic and atheist (and Buddhist!) who would not accept the idea of the first principle being invoked. I fear they embody the religious bigot's conception of atheism - those who cannot be trusted, because they go so far in renouncing the moral idea of God that they deny existence itself. That is, these nonbelievers seem to be solipsistic, in that their beliefs don't appear to have room for others, except as illusion or a sort of divorced extension of their own selves. The fear is that they subscribe to a species of philosophical sociopathy. You don't need a belief in God to be a moral person, but you do need to believe in other people.