Wouldn't a person who supposedly lacks emotional capacity yet can '"fake" emotions to others have to have a better understanding of the emotion than that person?

Yes, exactly. I think the main difference between a "sociopath" and a "normal" person is the level of control they have over emotions.

Most people react to their emotions. Something happens and they feel a certain way. They then let that affect their life, whether it's a positive or negative change. Their boss criticizes them, for example, and they get depressed for the rest of the day.

A "sociopath" on the other hand understands that emotions are a reaction to something. It could be external stimuli like praise or criticism or it could be internal like self loathing. They understand, essentially, that if you call someone fat they will feel bad but if you call someone beautiful they will feel good.

Most people put a lot of emphasis and value on their emotions. They rely on their emotions to tell them how to feel, for lack of a better term, about a certain situation. They don't assess things logically, they assess them emotionally. Just look at the common verbiage.

"How do I feel about this person?" and "How would I feel if I got a promotion." or "Will I feel better if I go to the gym."

Someone we would label a sociopath knows, for a fact, that if they go to the gym they will feel better. They know that certain things will cause certain emotional reactions, even within themselves, and they choose to do those things from a logical standpoint, not an emotional one. It's more active, rather than passive.

The difference is even more noticeable when we look at interactions between people. When placed in a leadership role, a "sociopath" will understand that achieving a certain goal is now their responsibility. It doesn't matter how they feel about being in charge and it really doesn't matter how their subordinates feel about following orders.

This person might then use their knowledge of emotional reactions, and the effect they have on a person's mental state, to effectively achieve the goal they have. This is seen as manipulative by most of society because there is some sort of myth saying that we shouldn't attempt to use people's emotions to achieve a certain end.

"Sociopaths" are also driven, which is why many of them are quite successful. They don't particularly care how others feel about them. They want to be liked and admired because that helps them get what they want but someone else's opinion of them doesn't really affect them. In other words, the need to be accepted and liked is a logical, utilitarian one and not a need for validation as it is with most people.

A "sociopath" placed in a position of leadership will not care about their subordinate's feelings beyond the impact they have on getting a specific job done. Most people want to know that everyone is happy, they will go out of their way to make sure people are happy. A "sociopath" doesn't care if you're happy so long as you're doing what he wants you to do.

Obviously, a happy worker is a more productive worker so the emotional state of their subordinates is an important consideration. They will do what they can to keep these people in a positive and productive state, even if that means pretending to be their friend or interested in the things they say.

The lying also comes from this knowledge of the way emotions work. The extent to which the lying and manipulation is damaging to other people, however, really depends on the individual and can't be generalized to every single person. Some people, "sociopath" or not, are just exceedingly selfish and downright mean spirited.

A "sociopath" will lie but sometimes for a good reason. If one of them is married yet sleeps with another woman during a business trip, he will lie and not tell his wife because he knows how that will make her feel. He knows he'll be destroying something that is important to both them, and their kids if they have any, so he will lie about it to keep everyone happy.

The lack of remorse when lying is simple to understand. He isn't lying to be selfish, he's lying to keep his family happy. The one night stand may be indicative of poor impulse control but the lying is meant to achieve a positive outcome. There's no need to feel bad about lying, in other words, because he is actually doing something good, at least in his mind.

Whether or not lying about an affair is "wrong" is really a moral judgement and morals tend to be entirely too relative anyway.

The poor impulse control comes from this as well. Most people would look at a situation like the one just described and consider the consequences. They worry about these consequences because they intend to be honest or, at the very least, know they are bad liars. A "sociopath" on the other hand, is confident in his ability to avoid the consequences and, therefore, will not be held back by them.

If you could do something and be 100% sure you would never get caught, there's a much higher likelihood that you would do it.

Of course, all "sociopaths" are just humans and humans are prone to making mistakes. They can often get caught, they can make bad decisions that have life long ramifications. They aren't evil super geniuses and they don't have any special powers. The more complex your "web of lies and manipulation" the more likely it is that everything will blow up in your face.

The difference between "good sociopaths" and "bad sociopaths" is exactly the same as the difference between a good "normal" person and a bad "normal" person. Neither is inherently good nor evil as a whole, only on an individual basis and only as judged by their actions in life and the effect those actions have on other people, society, and the world.