You can repeat it but it doesn't make it true. which it ain't. There's a document from the State Department posted on this thread proving this.
the fact of his birthright claim
His claim is more statutory than "birthright," assuming his biological and legal father is the British subject he says it is.
I am simply advising you of U.S. citizenship law as it was written, applied and generally understood in the sixties.
A minor child could not renounce his birthright claim to U.S. citizenship. Nor could his parents. Or anybody else. Period.
If you prefer to ignore this fact because it doesn't suit what you want to believe, you are welcome to do so.