It does feel like bad guys really don’t think this sort of thing through before they do it. They seem to lack the predictive skill that most of us use to prevent us from murdering people in our way. Most of us can imagine how we’d feel after murdering someone or at least can imagine that we would feel a weight eventually. We can predict our own behaviors and responses and this is very likely one of the things that prevents us from going around murdering one another. Morality, sure, and all kinds of other social constraints but ultimately we’re probably more concerned about how our own consciences would sting us than about the right or wrongness of our acts.
This predictive skill, the imaginative leap around feelings is one of the major things missing in a psychopath. He cannot imagine what other people feel and cannot empathize. He likely also cannot predict his own emotions, should he have any.