Even if cops were just a totally random selection of people from the general population, the fact that there is effectively little-to-no oversight, both in terms of law/institutions and in terms of social shame, means that anyone who isn’t a bastard before going in is extremely likely to become one, even absent all those other factors like cops becoming more insular and separated from the civilian population (“thin blue line”), the militarization of police (though no need for discipline, apparently), and sickened internal department policing cultures.

And cops are generally picked from a pool even less suitable than a totally random selection from the general population.

Power tends to corrupt, absolute power corrupts absolutely.