When I engage in the defense of my country (or my sons do) out of a "sense of duty", that is a choice. I don't understand how you could possibly claim it to be anything else. And, selfishness is not a virtue. It is a narcissistic act of self-preservation which usually has resulted in anything but. Just ask those who "selfishly" served their selves during the Revolutionary War by fighting on the side of England, and who then suffered the consequences of their acts of selfishness.
Yes it is a choice, and that's why it was an obligation you chose to undertake, not a duty someone put upon you. That's the difference.
If you're a christian, then obviously it's not a virtue. I don't operate under the christian value system however and selfishness is a virtue under the one I do follow.
Look at it this way, when one fights for their country, should they do it for themselves or out of a sense of obligation to others?
I've been serving for 23 years in the Army (as of this coming January) and have loved almost every minute of it. And, moreover, for entirely selfish reasons. I love this country. I love our way of life. I love that my family can enjoy the freedom this country offers. I love knowing that my son respects our flag and knows the sacrifices servicemen make to keep this country free and safe.
These are purely selfish reasons. There is a distinct difference between irrational selfishness (near-sighted, short term) and rational selfishness (long term). Most rationally selfish people will see the personal (self) value of preserving this great nation for their benefit and that of their loved ones (also purely selfish).
The term selfishness has been tarnished by the leftists/statists to mean anything that is even slightly for the benefit of one person as being bad and ammoral. If something, like serving this great country, means so much to ME that I'm willing to put my life on the line for 23 years, it must mean something to me- therefore because I'm selfish I've been a soldier. If this country meant nothing to me and I still wore the uniform, I'd be doing the selfless act for something that holds no importance to me.
I do prefer to have "in God we trust" on our money, but I find preserving the Constitution profoundly more important. I love this forum for discussing different points of view.
I also spent many months (out of almost 13 years of being in Europe) at Hohenfels and Grafenwoehr. My favorite exercises were the NATO exercises with the other services. We'd always gripe about the other militaries being able to have long hair and pot-bellies, which became apparent disadvantages in real missions... ;-)
Have a great evening.