I think if 1 out of every 5 cops are bad there would be many more instances reported in the news. Sure there are incidents that are not reported and there are certainly bad cops. But there are 800,000 cops in the U.S. If you look at all of the undisputed incidents where a cop did something dumb compared to the actual number of cops I think you would see numbers are actually quite phenomenal.
Many of us are at odds whether an incident is undisputed. Michael Brown, no doubt, he earned his, there are others that are undisputed by the police, but disputed by the many in the public. I do not think that it's unbelievable at all that one in five people in any profession are in the wrong profession.