Police officers are, essentially, the enforcers of the law and of what their country defines as justice. As such, their use of power should be matched to the situation at hand and to what is accepted by the authority they enforce, as justice. Without this balance, the police will either become incompetent at their jobs, or state-funded thugs, defined by their disproportionate brutality.
Unless the country is some sort of a peaceful paradise, police work will remain far from easy. There are so many values to preserve properly while on the job -- lower corruption, prevent avoidable deaths, detect criminals, endure harsh criticism from basically everyone, and so on. The police officers better not become corrupt themselves, or they will only enforce what they are required to oppress.
In other words, being a local executor of justice will not always be rewarding beyond the pay itself. The police officer stands within a constant dilemma -- why serve a nation, or people, that constantly degrade and shame me, despite all the hard work I'm putting in the name of the law?
We humans do not tend to praise those who stand in our way, whether or not our endeavors are legitimate. We will praise those who make us feel good, even if said feeling is against us, like in the state of unhealthy addictions.
But many of us will condemn, degrade and belittle those who will try to stand in our way, even if their opposition is for our own good. In other words, we humans seek good, but not always the good that is within our best interests. Thus, the folk that'll try and block us, even if they're just doing their job, will be hurt by some of us -- not necessarily within the verbal area exclusively.
Is the police force good? It depends on 2 questions -- whether or not the "Justice" they represent is good by widely-accepted standards, and whether or not its representatives are doing their jobs competently. And by "competently" I also refer to avoiding unnecessary brutality. Only that way one should be able to determine whether they are being punished/arrested for the sake of common good, and whether their punishment/arrestment is justified, even if it is, overall, uncomfortable.
In the end, like any other government or elected officials, the police force are basically servants, even if their service is to be attacked or questioned. Without their existence, there would be little fear to commit crimes from both the potential criminals and the criminals themselves. Even if we don't like them or their methods of execution, they are there for the safety of us and for the authority of the State.
Without enforcers, a society will essentially be an anarchy. As without actual power from the government, it will be ineffective. And even peaceful countries, such as Lichtenstein, have a police force.
That is, of course, assuming that countries are a necessary tool for survival, and thus, existance. Giving that we need money in order to survive within civilization, I would like to argue that countries need to exist, least because they are financial institutions.
The worst kind of police force is one that does not put their servitude above every other interest while on duty. If an officer receives a bribe from a criminal in addition to their existing pay, they should consider finding a job with higher pay, in case they won't come clean with their own violation.
The payment is the incentive to the job, and the incentive loses its functional worth if the worker does not do the job as expected from them. Why should the State fund an officer that takes even more payment, while not doing their job as expected?
Thus, corruption is to be dealt with in the name of competence.
Rebellions, unless moral and just, should not happen in a state that allows the freedom of protest and provides the citizenry the potential to grow and live decently. This is why one should try and rebel in North Korea and not in any other liberal country.
Because the officer is always under potential of constant examination from both civilians and the authority, morality is something that should be in a higher priority than the pay itself. Why? Because even if you are in a corrupted force, at least try and give an individual example of proper justice. That way, no one will blame you for following and imitating the wrongdoers, as did Adolf Eichman, a senior Nazi official, who, in his defence, had simply claimed that "I only did what I was told to do".
Thus, those who consider becoming police officers, should consider not only the pay, the safety and so on -- but also whether or not they are prepared enough to follow their authorities' view on what "Justice" is and what "Justice" entails. Finally, should you disobey in the name of your own justice -- prepare to either defend yourself, or flee the country afterwards, just as Eichman should've done instead of following the very orders that made him the very first executed man of Israel.
If you care for morality as well as your pay, consider being a police officer only for a police force that is as least corrupt as possible. That way, you will increase the chances of being corrupt yourself.
Read more on Adolf Eichman on this external source.