The psychological literature on "evil" generally leads us to one thesis: Most of us become evil. See, e.g., The Lucifer Effect: Understanding How Good People Turn Evil (here).
While there are sociopaths among us, most of us are socialized into being law-abiding and mostly decent. Put in the right situation, we can become evil. A fun illustration is with the Stanford prison experiment - which was chillingly depicted in Das Experiment. (You must rent The Experiment, which is available on Netflix.)
What's all of this got to do with Section 1983? It has everything to do with Section 1983.
Police officers do not start off evil. Yet officers regularly brutalize civilians and lie in court - so-called testilying. Even the "good" cops do nothing to stop the bad cops, instead acquiescing to the culture of corruption. One reason good cops go bad is because pressures from on high.
In this insightful interview with ABC News, an on-the-beat cop explains how police quotas lead to false arrests and wrongful convictions. Anyone concerned with our judicial system should check out the story: