Talk about frightening overtones of 1984. When "voluntary" is used to describe a mandatory action and when the Left agitates for Congress to pass a mandatory national service bill, we're in the same ideological territory as Communist youth indoctrination groups that all countries behind the Iron Curtain had.
The people of the United States are the most charitable of any in the free world (per capita private donations in the US are orders of magnitude higher than those in any other developed nation) and are the most generous with their time despite the longer working hours that Americans experience (do YOU have a government-limited 35-hour workweek? neither do I). But the universal service mandate would take away the incentive to perform private service by making charity, community outreach or other "service" a mandatory act. There is no better way to ruin the generosity of spirit and the rewards a person receives from doing good deeds than by making such actions required by the government.
It's just unAmerican.