Do you think people opposed to the war don't volunteer with USO? We certainly do, it's not a partisan organization. In my experience most people who've volunteered with them had the same motivation I did, i.e. having had family in the military (or having served themselves), which obviously includes people from both parties.
Do you really see it as an American citizen's duty never to call for an end to a war, no matter how poor the returns on lives lost, no matter how deep the quagmire, no matter how blindly reckless the Administration? I can understand that it's a far better feeling to leave home confident that few will see any of the sacrifices to come as wasted or in vain. But to turn that into some sort of trump card against other citizens' obligations to vote their consciences on the overall results of the war as they best understand them--that to me seems antithetical to democracy.