Estel,
The thing that has saved the US military, even after we became an all-volunteer force, is that we (most of us anyhow) actually trust our government to employ the military in legitimate situations. Sure, individuals will always question the value of a war, but time and again Americans have stepped up to fight when called to do so by their country.
If that's too strange of an idea, just consider the US Civil war. In that war, households were torn apart as people turned to their sense of moral obligation and came up with different answers. Some chose a loyalty to local or regional obligations, but a great number chose loyalty to the concept of a nation made up of many states. The union won, and to this day when that union raises the call to arms, people respond.
That trust may be lost in the future, but for now Americans still trust that their blood will not be spent by their elected government on useless or trivial endeavours, and that the government, once it has sent citizens into combat, will not abandon those citizens. Our enthusiasm for combat does not come close to the fanaticism displayed by various groups around the world, but what we lack in bloodlust we make up for with a passion for technical excellence. That makes the US military extremely effective from both the tactical and National Strategy points of view.
Give us a reason to fight and enthusiastic leadership, and the average US Soldier/Citizen becomes a match for any troop in the world in terms of both competence and "guts". Blame it on a constitution that pretty much guarantees that the average person MATTERS... Sure the US doesn't have a radical national religion to bolster our courage and tell us that we're destined to rule the world, but the constitution is a pretty good alternative.