What does "serve your country" even mean? I always thought it was a stupid phrase.
A nation does have interests, though lately that's become synonymous with the Federal Government having interests. In case of invasion, one serves the country by defending its borders and people. In case of attack, one (theoretically) serves the country via retaliation against the responsible party/parties, and the bringing of culprits to justice. In case of attacks against an ally, one (theoretically) serves the country by rendering aid to that ally and, potentially, assists in offensives against the attacker. Those are basic scenarios.
Now, the reality is that the US is not likely to be invaded by a nation anytime soon, so the first scenario is out. Additionally, that function can be served by the militia and other domestic outfits rather than the huge number of troops our various branches of the military have.
The next reality is that the Government defines the attackers. Again, we are unlikely to be officially attacked by a nation. This is how we've gotten so deep in the "War on Terror"; we are battling a technique in several nations, and ignoring the nations of origin for some of the actual attackers.
The last scenario is, again, defined by the Government. Who is an ally worthy of shedding American blood? The People don't get to vote on that, and probably don't even think about it much. The conflicts are framed so neatly that most of the population would think it's the US's idea, and in our best interests. The US often assists its allies only to find them as enemies a decade later.
All of those things aside, though, the Government puts out these orders, acting on behalf of the People (allegedly), so to carry them out without regard for self is service on behalf of the country.
I do believe putting oneself in harm's way is a difficult thing, especially at the age these people are doing it. The orders aren't their fault, and many go through their tours without mowing down innocents or committing crimes of other sorts. They're just people. They grow up to be Gunny or Kokesh or Ron Paul or Dennis Franz or Elvis Presley (though I don't care for him and his stolen hits) or Jesse Ventura or any number of others.
I always liked this way of looking at it:
[P]atriotism... is not short, frenzied outbursts of emotion, but the tranquil and steady dedication of a lifetime. ~Adlai Stevenson
We're the true Patriots

"We" include those who've served, came home, and merged their views with the fight for Liberty at home.