Please note that the following excerpts are from the 1974 paperback edition of the book. Heilbroner subsequently updated the material at least two times.
Some of that prediction [by Marx], it should be noted, has been validated. The dynamics of capitalism did bring about a steady forced migration of farmers and self-emplyed small proprietors into the ranks of wage and salary workers, and the pronounced instability of the system did genererate recurrent severe economic hardships. What seems to have forestalled the final vindication of the Marxian prognosis, however, was a series of developments that offset the revolutionary potentialities envisaged by its author. One such offsetting tendency was the steady augmentation of per capita output, which effectively undercut the development of proletarian feelings of exploitation. A related development was the rise of a "welfare" framework that also served to defuse the revolutionary animus of the lower classes. Last and perhaps most important was the gradual discovery -- a discovery both in economic techniques and in social viewpoint -- that government intervention could be used to prevent a recurrence of the near-catastrophic collapses suffered by the laissez-faire versions of capitalism characteristic of the late nineteenth and early twentieth centuries. [p.67]
Those who are currently advocating a dismantling of the "welfare" system in place might want to consider the consequences of such a move.
Finally, the failure of the conservative prognosis may simply signal the possiblility that whatever its economic strengths, the social ethos of capitalism is ultimately unsatisfying for the individual and unstable for the community. The stress on personal achievement, the relentless pressure for advancement, the acqusitive drive that is touted as the Good Life -- all this may be, in the end, the critical weakness of capitalist society, although providing so much of the motor force of its economy. [p.70]
But I think the evidence, even including these latter nations [Czechoslovakia and Yugoslavia], is sufficient to enable us to assert that the economic success of industrial socialism, in and of itself, has not brought a corresponding rise in general "happiness" or social contentment, much as with the mixed record of economic success and social disappointment of capitalism. [p.75]
For industrial civilization achieves its economic success by imposing common values on both its capitalist and socialist variants. There is the value of the self-evident importance of efficiency, with its tendency to subordinate the optimum human scale of things to the optimum technical scale. there is the value of the need to "tame" the environment, with its consequence of an unthinking pillage of nature. There is the value of the priority of production itself, visible in the care both systmes lavish on technical virtuosity and the indifference with which both look upon the aesthetic aspects of life. All these values manifest themselves throughout bourgeois and "socialist" styles of life, both lived by the clock, organized by the factory or office, obsessed with material achievements, attuned to highly quantitative modes of thought -- in a word, by styles of life that, in contrast with non-industrial civilizations, seem dazzingly rich in every dimension except that of the cultivation of the human person. The malaise that I believe flickers within our consciousness thus seems to afflict industrial socialist as well as capitalist societies, because it is a malady ultimately rooted in the "imperatives" of a common mode of production. [p.77]
But at this juncture in history, our attention had better be focused on what men are likely to be, rather than on what they could eventually become. The human prospect forces us to deal with human change within an indeterminate, but not indefinite, time period, and speculations as to the degree of potential change must give way before the degree of change that is imaginable within that period. [p.120]
[Quoting Bertell Ollman:]
People acquire most of their personal and class characteristics in childhood. It is the conditions operating then, transmitted pimarily by the family, which makes them what they are, at least as regards basic responses; and, in most cases, what they are will vary little over their lives. Thus, even where the conditions people have been brought up in change by the time they reach maturity, their characters still reflect the situation which has passed on. If Marx had studied the family more closely, surely he would have noticed that as a factory for producing character it is invariably a generation or more behind the times, producing people who, tomorrow, will be able to deal with yesterday's problems. [p.121-122]
It is the challenges of the middle and the long run that command our attention when we speculate about the human prospect, if only because those of the short run defy our prognostic grasp entirely. It seems unnecessary to add more than a word to underline the magnitude of these still distant problems. No developing country has fully confronted the implications of becoming a "modern" nation-state whose indutrial development must be severely limited, or considered the strategy for such a state in a world in which the Western nations, capitalist and socialist both, will continue for a long period to enjoy the material advantages of their early start. Within the advanced nations, in turn, the difficulties of adjustment are no less severe. No capitalist nation has yet imagined the extent of the alterations it must undergo to attain a viable stationary socio-economic structure, and socialist state has evidenced the needed willingness to subordinate its national interests to supra-national ones. [p.130-131]
When men can generally acquiesce in, even relish, the destruction of their living contemporaries, when they can regard with indifference or irritation the fate of those who live in slums, rot in prison, or starve in lands that have meaning only insofar as they are vacation resots, why should the be expected to thake the painful actions needed to prevent the destruction of future generations whose claims to life can be honored only by sacrificing present enjoyments; and will they not, if it comes to a choice, condemn them to nonexistence by choosing the present over the future? [p.143]