By comparison, have you ever had a really positive experience with the dentist?Not the OP, but yes. All the time, in fact. Then there's also the crucial difference that going to a dentist is a voluntary exchange, whereas being stopped and frisked by police is an unsolicited act of aggression no matter how you put it.
...successful crime prevention means locking up our families and neighbors
Hardly. Locking up families and neighbors is the exact opposite of crime prevention. It's treating the aftermath. Crime prevention should be analogous to preventative medicine: minimizing the possibility of it occurring to begin with.
Police by definition are reactionary agents. They don't have the competence or the will to do anything other than handle aftermaths and create intimidation in a dubiously effective attempt to scare off bad guys.
This isn't to say there aren't bad cops, but they're a tiny minority of all cops and largely reflect their communities.
Pareto principle: 20% of people do 80% of the work, or in this case make most of the difference. It's also the reason why "Not all -ists are like that" arguments don't work: they fail to realize that minorities in an in-group can still be highly influential and destructive.
Isn't it weird how there are no bad Canadian or Swedish cops?
They aren't typically covered in international media. You don't see any bad Serbian cops too often, either. Do they not exist?