This is a very insightful article that speaks to a deep understanding of the antisocial mind; ASPD and psychopathy aren't the same thing though, and using them interchangeably further muddies the understanding of both.
Because of how these conditions are studied, and because psychopathy isn't listed independently of ASPD/DPD in the DSM or ICD, the two are often used interchangeably–even by some clinicians. A lot of data for both have historically been collected from incarcerated populations, skewing the understanding of both disorders towards a criminal presentation and blending the understanding of one into the other.
The main differences, briefly, are that people with ASPD are more erratic and impulsive due to growing up in very violent, competitive, or neglectful environments while bottling up their emotions. This causes a child who will go on to develop ASPD to inhibit their emotions via a number of psychological defenses such as repression or rationalization (He deserved to be robbed because he was flaunting his money in a dangerous area. If I hadn't robbed him, someone else would have.) in order to defend themselves against the guilt, shame, or regret associated with their actions.
A psychopath might say the same thing if they were questioned about the robbery, but the response isn’t fulfilling the same purpose because, if they hadn’t been asked, they likely wouldn’t have any conscious justification other than that they were an easy mark. It isn’t a defense against emotional pain, it’s a defense against being identified as having psychopathic traits. Based on DSM criteria for ASPD, someone could be diagnosed with the disorder based entirely on a history of crimes that they committed to fulfill basic resource needs or provide for their family. They may have initially felt guilt or shame for committing these crimes, but eventually, their defenses become so well-developed that they appear to be psychopathic on the surface. This is the trouble with studying personality disorders based mostly on observation of behavior; it’s very difficult to distinguish between true, neurologically shallow affect and repressed affect without expensive fMRI scans.
Psychopathy, on the other hand, is neurodevelopmental in nature. Someone high enough on the psychopathy scale has no need for psychological defenses in the same way that someone with ASPD uses them as a defense against guilt, regret, or empathy, because they don't feel emotions strongly or long enough for them to register as important. Childhood environment plays a major–yet different–role here. Someone born with a strong genetic disposition towards psychopathy can't change the primary traits associated with it, but their environment growing up determines how severe the disorder becomes in terms of secondary (behavioral) traits. If someone with primary psychopathy grows up in an environment like the one I described above, the result will likely be a truly ruthless, criminally flexible psychopath. Extreme ASPD, essentially (ASPD with psychopathic traits). However, if this same person grows up in a safe, functional, loving family environment and learns that working with others–or at least appearing to–is a better strategy, they are more likely to go on to excel in a field that either doesn't require or rewards a lack of affective empathy–politics, business, law, media, or even some medical specialties like surgery–but will likely still face major difficulty maintaining close relationships due to emotional coldness and lack of empathy.
As you point out, nobody is totally immune to negative emotion–even psychopaths; however, the shallow affect (including empathy) that defines and distinguishes the disorder from ASPD means that any guilt or regret that a psychopath might feel for hurting someone isn't strong enough or doesn't last long enough to cause them to consider changing their behavior. What a typical person might experience as profound grief, a psychopath would probably experience as a low mood that they’d get over quickly. With regards to guilt and shame, as you mentioned in another article, experiencing these emotions would be an almost entirely cognitive process dependent on their relationship to those affected by their actions. Because so much of their emotional experience is cognitive, their reaction to the distress of others is highly dependent on the strength and nature of their attachment to their parents or other significant childhood figures. This attachment is what informs a psychopath’s opinion of and desire for relationships with others, and by extension, their willingness to adapt to their emotional needs. A sufficiently pro-social psychopath might apologize or take other steps to repair a damaged relationship, but only because they value the relationship, rather than because they are truly remorseful.
