The idea and ideal of the citizen-soldier has been at the core of democracy since the ancient Athenians invented it and entrusted the defense of their city-states to their hoplites, the first citizen-soldiers. Divide citizenship from military service and something essential to the preservation of democracy since the Greeks has been lost. Democracy and its defense will have been separated, and that is not a wholesome arrangement for either. To quote Thomas Jefferson, "Every citizen should be a soldier. This was the case with the Greeks and Romans, and must be that of every free state."
A professional army is a great asset -- a necessity, as many a democracy has discovered when it neglected to train one. But a republic needs citizen-soldiers, too. Without them, democracy is divided at its very core: between those who defend it and those who are defended.
It is not a healthy division, for the result is a mutual ignorance that leads to mutual estrangement -- between those citizens who have known military service and those who haven't. It is a division no democracy can afford. For the military needs a connection with the citizenry, and the citizenry with its military. Both benefit, and the country benefits most of all.
Or as Gen. Dempsey noted: "When you have one part of the population that is designated as warriors and another part that is designated as something else, I think that disparity begins to establish a psychology...." And it is not a healthy psychology, for it divides rather than unites. And united we stand.