I think I'm a pretty great cyclist, and by great I mean that I know when to do what, and consider my impact on those around me as much as myself.
The problem here is this is just one example of the problem with police abuse in general. Police should be capable of not defaulting to biases against groups of people because they need to be by their job description. Whether that's "all bikers are entitled and actively dangerous" or "all blacks are suspicious unless otherwise proven", the sentiment is the same. They must be held to a higher standard of judgment because of the authority they are given.
PS - If everyone gave up cycling because they didn't want to be associated with those who do it poorly, not only would that be a shame, it'd leave nothing but the belligerents you speak of.
Do people commuting on bike in Chicago kill more people than commuting in cars?
Maybe the OP is a great cyclist. Maybe he's not. It's immaterial.
What is material is trying to provide some context into why that happened, if it did. Lets just say as a fellow Chicago resident I also immediately had the same suspicions that you were responding to.
I used to commute daily as a cyclist, until I moved here. I sold my bike, as I don't want to be associated with these people whatsoever. They are the most entitled, aggressive, and actively dangerous group of commuters I've witnessed. I've lived in Amsterdam. This is not how bikers should behave.
So to me, it was simply providing context to those who don't live here for stories that don't make any logical sense. Cyclists here get absolutely zero benefit of the doubt from me, and I imagine that attitude can get into a cop on a bad day as well. Certainly doesn't justify it, but it explains it.