Everyone who enlists into military service implicitly agrees to serve in combat. You go where you are told to go and do what you are told to do. It is possible to enlist for an MOS (or branch of the service) that makes you extremely unlikely to see combat, but there are no guarantees. I saw many personnel clerks, supply clerks, and cooks doing guard duty overnight in Vietnam, where the dangers were analogous to what combat soldiers saw.
The U.S. is not just a country like Latvia that can focus all of its "defense" energies on fighting territorial threats on its own borders. We are a global force for peace and security, and have signed numerous treaties that oblige us to protect and defend the people of scores of nations if and when they are threatened by outside governments. Thus, our military people and assets can be called upon to defend the people of any number of countries from threats, both internal and external, as required by these treaties and constitutionally by our Congress and/or President. And YOU, PERSONALLY are responsible for these military obligations and undertakings because YOU, PERSONALLY either voted for the political office-holders, or you are obliged by law to live by their decisions under our democratic republican principles of governance.
Anyone signing up for military service is presumed to be aware of these realities.
Like it or not, EVERY U.S. legal resident is subject to conscription into the military service. The Federal Government has elected to staff our armed forces with volunteers, but this is merely a temporary policy choice that could be reversed on a moment's notice through action by Congress and the President. If the number of volunteers is ever insufficient to accomplish the missions we have undertaken, or if we are invaded by overwhelming military forces, you can be certain that the military draft will be re-instituted, and you can also rest assured that such an action is entirely legal and Constitutional. YOU could be obliged to serve, against your will, or be incarcerated for not doing so.
So it is not completely fatuous to understand that because there are enough people who voluntarily enter military service, YOU, PERSONALLY, are off the hook for that service. Otherwise, you, personally, would be subject to the military draft. And this applies whether you are male, female, "Black," Hispanic, or homo-*******-sexual.
So it is entirely appropriate for you to thank soldiers and sailors whom you encounter for their service, you pathetic ingrate.