In the 1840's, Henry Clay of Kentucky was the most prominent and influential Senator. Though he owned dozens of slaves himself, he was ideologically opposed to slavery, and proposed a compromise solution: Let the U.S. government buy every slave at fair market value, and give them their freedom. (The importation of slaves had long ago been outlawed, so this would have put an end to legal slavery in the U.S.)
On the one hand, it seems utterly immoral to reward people who have purchased another human being as if he were a horse or a tractor. On the other hand, it might have saved 600,000 human lives and avoided the trauma and embitterment that war engenders, passed from generation to generation to this day.
Upton Sinclair was a social reformer and prolific author in the early decades of the 20th Century. This was a time before the ruling class had so firmly established "socialism" as a dirty word, among intellectuals and workers alike there was a sense that a socialist uprising in the U.S. (peaceable or violent) was a real possibility. There were socialists and communists and anarchists and syndicalists, all promoting their various radical agendas, but what they had in common was democratic control of the corporations by working people.
Sinclair regarded this transition as inevitable in the long run, because he saw the contradictions inherent in capitalism. The simple fact is that because the aggregated workers' salaries are only a fraction of the retail price of the goods they produce, the nation's total output can never be sold without foreign markets and imperialist wars. (Sinclair never considered that America's imperialist wars might be continuing 90 years into the future, nor did he count on the effectiveness of the long-term propaganda campaign that would keep workers convinced that organizing as workers was not in their interest.)