It is a fact that giving someone a position of power or authority has serious psychological effects. It makes the person that wields power ignorant, hypocritical, immoral, violent, sociopathic, etc. Also, positions of power within hierarchies create situations in which almost any individual will commit any atrocity imaginable so long as they are told to do so by a superior. Also, conditions in which people are given arbitrary authority over others cause the wielder of authority to abuse their power and torture and mistreat those over whom they have power. Any career politician or cop WILL become pathological, more ignorant, and immoral. The character and integrity of the person does not matter. It does not matter if the individual is a scientist, an activist, a saint, or a kindergarten teacher; they will become idiotic sociopaths, pathological liars, and pathologically aggressive—even to the point of committing genocide, murder, or rape—, if they happen to be placed into the right situation and given specific authority and power relations to others.
The problem is not the cops, but the institution of policing. The problem is not the bosses, but the institution of hierarchical firms. The problem is not the money, but the accumulation of wealth that constitutes power and thereby corrupts the wealthy. The problem is not representative democracy or even the individuals who hold office, nor even the views and agendas of those in office, as much as the fact that allowing for the existence of power-wielding career politicians guarantees the negation and corruption of democracy. What we need is a fundamental reform of the institutions of our society, so that unnecessary power relations are eliminated. We need checks and balances to every single power.
The psychological, sociological, and anthropological literature backs this up. Check out the experiments, research, and writings of Stanley Milgram, Hannah Arendt, Philip Zimbardo, Dana Carney, Gerben A. van Kleef, Joris Lammers and Adam Galinsky, etc. The literature and research proves that giving people powers similar to those possessed by cops will make them behave in the most atrocious fashion. Cops kill innocent people and lie about it because they are given powers that they ought not to be given, and their powers are not appropriately checked. The institutions are flawed and create injustices. It isn't the case that the individual cops are just bad apples. In reality, the apples go bad because they are placed in a moldy barrel! The same goes for politicians.
"Blind obedience to corrupt authority is a mental disorder. That is not a euphemism, but a fact. There is a prevailing view in many societies that this thing, called the government, wields absolute supreme authority. In its wrath the State can smite their enemies, and enforce their prejudices. In its mercy it can heal the sick, and feed the poor. In its power it can turn paper into gold, or even change the weather. These people believe that society is the product of centralized violence, and not the aggregate of their own decentralized decisions. Those who deeply internalize 'obedience to authority' as a core principle become capable of the worst forms of murder, and tolerant of the worst forms of abuse. They even chastise those who resist through horizontal discipline. But most importantly, they become capable of passively witnessing evil, and even facilitating it, believing, as Eichmann did, that their god absolves them of personal responsibility."—Davi Barker ("Authoritarian Sociopathy")