In Death Note the ring of Gyges story is presented with a twist, not only does having power corrupt, but that same individual, upon losing that power is shown to return to being a good person, and when they get it back they return to being corrupt. Of course such stories are only stories, we can’t say for sure how anyone will react to receiving such powers. But they seem believable because we often witness for ourselves how having simply political or economic power has the tendency to drag otherwise good people down.
So why does an increase in personal power result in unethical behavior? One possible explanation is that an increase in personal power results in the individual worrying less about being punished for their actions, and that without the fear of punishment holding them back they will follow their natural inclinations to act unethically. This is the explanation most often given for why power corrupts, but although it certainly it seems like a reduced fear of consequences might contribute somewhat to unethical behavior it seems unlikely that it can be completely responsible for the corrupting effects of power. Although people will act unethically some of the time when they think they can get away with it, they don’t in general try to get away with unethical behavior whenever possible. Rather it seems that people try to act ethically for the most part regardless of whether they will be punished, and that they only take the possibility of punishment into consideration during the occasional ethical lapse.
Another possibility is that increased personal power decreases the person’s fundamental motivations for acting ethically. Ethical motivations, I assume, come from the nature of belonging to a community; when you belong to a community you want what is best for the community, because you are a part of it, and hence you should act ethically. Thus ethics can be seen as a triumph of we-thinking over I-thinking. Increased personal power, we might hypothesize, has the effect of distancing people from their community, and increasing I-thinking at the expense of we-thinking. They might not feel like part of their community anymore, or that the community can do anything for them, and hence might cease feeling obligated to it, which would result in unethical behavior. But even this explanation seems incomplete, because it would seem to imply that people are more conscious of their reasons for acting ethically than they actually are. It is true that being part of a community does provide a reason to act ethically, and in fact some people may act ethically because of such reflections. But most people act ethically simply because they have been taught to act that way, meaning that acting ethically has become one of their motivations without them ever having an explicit reason for ethical behavior. Thus it seems dubious that their realization that they are not as closely connected to their community as they used to be will have much of an impact, since they probably don’t realize that it is their community that is the ultimate reason for acting ethically. In fact people who deeply believe that the reason to act ethically is because of divine command and divine punishment seem just as easily corrupted by power as other people are, and it is unlikely that they think that their increase in personal power allows them to escape the divine command or divine punishment.
The third possible explanation is that an increase in personal power gives the person new goals that seem ethical to them, but lead to unethical behavior. Certainly this seems to be what happens in Death Note, as the protagonist decides to eliminate crime by killing every criminal. Now these new goals may or may not be ethical in themselves, but they are generally more grandiose and more important than the goals the person had previously. And thus such goals may seem to justify acting at least slightly unethically, while the more limited goals that they had before did not. For example, in Death Note the protagonist ends up killing some of the police who are after him, because he realizes that if he is caught he will be unable to continue killing criminals. Since I am a consequentialist I admit that a sufficiently worthy goal may justify some amount of unethical behavior. The real problem lies in how people reason about the costs of their new long-term goals. If someone has a goal that they think of as being worth 10 positive units of goodness then they will see any acts valued at less then 10 negative units of goodness (unethical acts) as justified, given that they are done with the purpose of reaching this goal. And this may be acceptable reasoning. The problem is that over time such goals often require a steady stream of unethical acts. Each unethical act by itself may seem minor, and thus justified, but in total they may overshadow the positive results of the goal when reached. And this is aggravated by the fallacy of sunk costs, which in this case means that after having committed some unethical acts in pursuit of their goal people will continue to act unethically in order to reach it, even if the later unethical acts overshadow the positive effects of the goal, because they don’t want their earlier unethical acts to be wasted or unjustified. And thus the fact that an increase in personal power leads to the adoption of larger and seemingly more important goals means that it also leads to unethical behavior.