It's interesting that you focused on leadership/management as an option--no, I actually really am talking about going to the academy, learning about escalation of force, patrol work, and basic procedural law, and then manning the city streets.
I'm not expecting left-leaners to go in and "take down the corrupt cops from the inside", just to go in and do police work. Most cops that get away with murder don't appear to be nakedly corrupt or part of an overt/explicit conspiracy to commit murder and theft; they're just incompetent, malicious, and protected by the brotherhood.
I have the same criticism of left-learners in other fields, like business and engineering. I come from a very left-leaning community and family; they will talk up one wall and down the other about things like bank loan disparity, police response disparity, treatment by retail employees disparity, etc. but very few of them actually consider becoming a loan officer or a police officer or a grocery store owner and then choosing how to treat people that would normally be treated poorly. People in my familial and social circle want to work $70-100k white collar administrative jobs and tell everyone else how to run society, when it would be far more effective if everyone with their same viewpoints simply become part of society and ran it themselves.
More self-sacrificial behavior and working in "real" jobs would also solve a lot of problems with what I saw as a flaw in liberal/left thinking. It's hard to be friendly and forgiving to thieves and violent robbers when it's your retirement plan that's getting jacked up twice per year and losing a third of profit to theft and another third to taxation.