Great article !
Although I totally agree on your conclusion that we should focus on the good, I would advocate that the vagueness of the concept of evil is not what makes it politically useful.
In democracies, politicians must get general approval, so they must appear as doing good (the right thing). The efficiency of “evil” as a category of political discourse in this regards stems from subtle logical fallacies, by which casting the other as evil implicitly makes you the good one, thus ensuring support.
- from good and evil as intrinsically opposing sides, we tend to conclude that evil doers intrinsically allies with each others. The ‘axis of evil’ rethoric reinforces that idea.
- from good and evil being opposites (which is true), we tend to conclude that they are complementary, i.e. there is no other options, which is false.
Fighting evil guys does not make you the good one (ex. Hitler and Stalin) ; and not engaging in evil does not ensure you are doing good (Christians recon man also sins by omission).
Politicians however will continue to use these fallacies to their advantage until we hold them accountable for the validity of their arguments.