Robert Heilbroner was perhaps the most famous American socialist intellectual of the 20th century. His The Worldly Philosophers sold millions, making it the second-best-selling economics textbook of all time. In my Business and Economic Ethics course, we read and discuss one of his articles.
Here is a new-to-me quotation by Heilbroner, writing in 1980, about who owns what under socialism:
“[T]he creation of socialism as a new mode of production can properly be compared to the moral equivalent of war — war against the old order, in this case — and will need to amass and apply the power commensurate with the requirements of a massive war. This need not entail the exercise of command in an arbitrary or dictatorial fashion, but certainly it requires the curtailment of the central economic freedom of bourgeois society, namely the right of individuals to own, and therefore to withhold if they wish, the means of production, including their own labor.”
So: Under socialism, you do not have the right to withhold your labor. Your labor belongs to society. So compulsion may be used to ensure that individuals work for society. In other words, socialism is a kind of slavery.
Note Heilbroner’s “moral equivalent of war” phrase and that nations often use war as a rationale for conscription. The more general point for socialism is that, whether at war or not, individuals belong to society. They are seen as a product of society, as constituting society, and as the means of society’s continuance.
Twelve years later, Heilbroner did concede that as a matter of practical results, freedom has been superior to compulsion: “capitalism has been as unmistakable a success as socialism has been a failure.” But I do not know that he ever changed his mind about the collectivized, altruistic ethic that underlay his commitment to socialism.
That, I think, is the more important issue of our generation. Socialism is widely recognized to have been a practical failure, but we still have a huge number of socialist-friendly individuals. Free-market capitalism, by contrast, is widely recognized to have been a practical success, but we still have a huge number of hostile-to-capitalism individuals. That indicates to me that beliefs about morality are driving the debate more than are beliefs about practicality.
 Robert Heilbroner, Marxism: For and Against (W.W. Norton, 1980), p. 157. Also quoted in David R. Henderson, The Joy of Freedom, p. 47.
 Heilbroner, quoted by David Boaz in “The Man Who Told the Truth: Robert Heilbroner fessed up to the failure of socialism”, Reason, January 21, 2005.