"If once a man indulges himself in murder, very soon he comes to think little of robbing; and from robbing he comes next to drinking and Sabbath-breaking, and from that to incivility and procrastination"

Thomas de Quincey's quote provides a satirical and overstated commentary on the domino effect of moral deterioration. The underlying message reflects the 19th-century concerns about the progressive nature of wicked habits. De Quincey humorously recommends that when a private commits an egregious act like murder, their ethical compass is loosened up, leading them down a path of significantly less severe yet still condemnable actions.

At first, the quote posits that delighting in murder will desensitize a person to dedicating other criminal offenses, particularly robbery. This development suggests a loss of moral restraint; as soon as the most extreme ethical boundary is crossed, lesser offenses become unimportant. The shift from robbery to drinking and Sabbath-breaking introduces a shift from criminal acts to habits considered as vices by the social and religious requirements of De Quincey's time. Sabbath-breaking, in particular, signifies a neglect for spiritual observance, showing a deeper ethical and spiritual decay.

The last step to "incivility and procrastination" parodies the trajectory from serious criminal offense to minor social faux pas, highlighting the absurdity of dealing with these behaviors as equivalent in moral weight. Incivility shows a breakdown in social custom-mades and respect for others, while procrastination suggests a failure in personal discipline and responsibility. By ending with relatively benign faults, De Quincey underscores the ridiculousness of equating murder with small ethical failings, thus critiquing the notion that allowing oneself one transgression undoubtedly causes a total moral collapse.

In essence, De Quincey's quote is a satirical take on moral absolutism and the fear of ethical domino effects. He uses hyperbole to question the idea that all sins and societal infractions are inherently linked in a chain of intensifying misbehavior. Through this lens, the quote serves as both an amusing reflection on morality and a critique of the propensity to overemphasize the consequences of preliminary ethical failings.