Jeff McMahan and others discuss at the Boston Review:
The military services in the United States have been organized on a volunteer basis since 1973, when President Richard Nixon abolished the draft. The end of conscription came as a relief to most people—to young men, their parents, and eventually the leaders of the military services, which had been plagued by internal dissent and a lack of professionalism, partly as a result of having so many unwilling members.
Though isolated voices have always challenged the shift to a volunteer military, their criticisms have recently become more widespread and more vocal. The main objections come from two quite different directions.
Some critics argue that the reliance on an all-volunteer, professional army has led to diminished public concern and vigilance with respect to the wars the government decides to fight. Limiting the burdens of military service to volunteers has, according to these critics, weakened inhibitions against the use of military force. When the Iraq War was debated in 2002–3, most citizens were not concerned that they or their children would be required to fight. This eliminated a powerful constraint against the resort to war. According to these critics, the reintroduction of some form of conscription is necessary to reestablish greater democratic control over the practice of war.
Other critics come from the ranks of just war theorists. Their concern is not with diminished public vigilance but with individual moral responsibility.