Actually, what I believe has nothing to do with it. The Declaration of Independence was a declaration of our national character. It asserts that this nation's legitimacy, indeed right to exist is rooted in the "laws of nature, and Nature's God," and that our Creator has endowed us with certain unalienable rights.
If one does not subscribe to those beliefs, by definition, one's beliefs about this nation's very raison d'être are at variance with those of the signatories of that document and the founders of this nation.
That does nothing to take away from your brother's service, nor any other self-proclaimed atheist that has honorably served this country. I'm sure he has his reasons for doing so. Perhaps it's to defend the nation that has allowed him and others of his persuasion to be true to their beliefs and prosper. Perhaps it's that and a combination of other things. I didn't say an atheist couldn't love the USA, only that the founding principles were inconsistent with their beliefs. I can love, appreciate and even defend organizations with whom my beliefs are at variance. That doesn't make me a member of that organization.
To believe that rights are bestowed by a power greater than man or government presupposes the belief that such a power exists. To deny the existence of such a power leads one to the conclusion that either:
a. No such unalienable rights really exist.
or
b. What rights do exist are extended to us by other men or governments.
This nation was founded on principles that are completely antithetical to either of those conclusions.
Because atheists do not believe in a God of Nature or a Creator, the Declaration of Independence does not apply to them? They do not subscribe to those beliefs, so they are still British citizens? My brother will be tickled to hear that and so will the guys he fights beside. His passport is all wrong!!! Perhaps the next time he gets a speeding ticket, he can use this argument.
I think Thomas Jefferson would disagree with you. I believe the Founding Fathers would welcome my brother and all other America-loving atheist patriots in with open arms.