"Good" isn't always subjective- there are certain absolutes.
It is never good to violate other people's liberty or property- except in self defense against aggression, or in defense of private property. Period. You may believe it to be "necessary", but it's not good.
If you picked the fight, it is not self defense.
If there is no individual victim, it isn't in defense of the innocent.
If your job requires you to violate other people's liberty or property, you can't be a good person while performing that job.
Police are required to violate people's life, liberty, and property by enforcing "laws" as a condition of keeping the job, and to continue receiving the paycheck (which is financed by violating property through "taxation").
Therefore, no matter how "nice" a cop may act, he can't be good and remain a cop.
There is no such thing as a "good cop".