They are very similar, yes, but synonyms will often have subtly different definitions and connotations that mean you can’t just replace one with the other wherever you want. Frankly, the difference between murder and killing is something I learned in high school English so I understand that the difference might have been off your radar before now, but this is the way the words are used most frequently, they’re different words for a reason. Murder implies a moral or legal judgement on the action of killing, and killing is just dispassionately describing that something has died as a result of some other action. We all learn something new every day, it’s OK not to know something.
The theory does not actually have anything to do with how many people are willing to abuse a gap in regulations for personal gain, it’s analyzing the dynamic between people who would abuse the system for personal gain, and that abuse causing a situation where people will enact vigilante justice against the first group. So people who are self interested will be less likely to abuse the system in ways that mark them as a target. All it requires is that the vigilantism is common and a known factor to the people abusing the system, so that the ways they choose to abuse the system are less obvious. Of course it could go any number of ways based on other factors, I’m just commenting on the dynamics of the interaction here.