One view of voluntarism is that it is uncompensated labor. People volunteer at a soup kitchen or in local service clubs. Well, by that definition, Americorps is not voluntary. Many Americorps workers signed on out of good will. But this does not set them apart from other workers.
Most entrepreneurs love their work.
They also desire the happiness of others. They try to give people something they want, whether it is a good meal, quality clothing, sturdy housing, or reliable letter delivery. In a market economy, the jobs of just about everyone pass this test. No one is forced to take a job. Capitalists could quit investing, bankers could quit lending, and workers stop working at any time.