Red Harvest offers a portrayal of the United States as a society driven by violence, greed, and a thirst for power. The true antagonists are not the gangsters, but rather the affluent and influential individuals who employ criminals to protect their often unscrupulously acquired wealth and influence. This craving for riches and authority surpasses even familial bonds, as demonstrated by Donald Wilsson's death, indirectly orchestrated by his father. Hammett raises the question of whether anything can be done to address this situation, and he also explores the repercussions for a man who chooses to avoid both the widespread corruption and the efforts to combat it.

The conclusion of the novel suggests that any triumph over materialism and greed will be fleeting, as the root of corruption lies not with the hired gunmen, but within the hearts of their employers—the supposed pillars of Personville's and American society. Thus, respectability becomes a mere facade, allowing the wealthy to engage in unethical behavior with minimal risk. The extensive bloodshed and brutality depicted in the novel are primarily endured by minor villains who become pawns in a power struggle they neither comprehend nor survive.

The Op, initially dispatched to Personville by his boss for a routine assignment, soon makes it his personal mission to clean up the city. He quickly realizes, however, that the usual methods of his profession fall short for this undertaking. To ensure both his success and survival, he must defy his superiors' orders; he has to lie, deceive, and even resort to killing. Ultimately, he understands that his success hinges on his ability to appear just as corrupt and immoral as the city's residents. By the novel's conclusion, he recognizes it's time to leave Personville, as he's alarmingly close to finding satisfaction in the violence and deceit. Despite being fundamentally honest yet ruthless, the Op is at risk of being tainted by the city's widespread moral decay. His most damning observation comes in the book's final parts when he states, "You can't go straight here."

The negative, anti-capitalist, and pro-Marxist stance is a defining characteristic of Hammett's work, especially in his early stories and novels. This perspective has significantly influenced many followers of Hammett in American detective fiction, notably Raymond Chandler, whose detective, Phillip Marlowe, is a more empathetic and less aggressive version of the Op. In Red Harvest, Hammett conveys the idea that a corrupt and materialistic society, willing to use any level of violence to maintain its immoral ways, can only be challenged by employing equal or greater violence and countering deceit with even more cunning deception. Legal solutions are ineffective—the police are often more corrupt than the criminals—and idealistic public defiance and the exposure of criminal activities prove self-destructive, as Donald Wilsson, the publisher of the town's two newspapers, learns.

Despite the Op's triumph, it is fleeting and comes with significant personal sacrifice. He realizes that the slain racketeers will soon be replaced. In achieving his victory, he has angered his superior, lost the esteem of his peers, and, most disturbingly, uncovered the "darkness of his own soul." He has also recognized how perilously close he is to the abyss that has already consumed the residents of Personville.