With luck we'll have the cops under constant scrutiny soon (sort of like what's been wrongly happening to us, the once-private citizen), and only then will we have an idea how to answer that question.
I've personally met many fine individuals that happened to be cops, so they do exist. But I will tell you without question that a culture of corruption exists in law-enforcement organizations all over this country. And as long as it exists, period, it is a huge problem.