For the record, the "police" involved in the incident were likely not the Chicago Police Department. They are the Chicago Department of Aviation Police (based on the one uniformed officer with the ball cap). They are trained law enforcement officers under Illinois law, but do not carry weapons (although technically certified to do so). The DOA Police have a... reputation... that is somewhat less than stellar. They are only found in the airside areas of the airport and are of the "run and hide" school of terrorist response.
http://www.cnn.com/2017/01/12/us/chi...tion-officers/
Any negative interaction with pax has the potential to become a viral PR disaster these days, regardless of who is responsible or what the facts of the matter are. I don't know if the root cause is the general lack of civility these days (which over-escalates situations), busybodies concerning themselves with matters that they neither understand nor have any facts to understand, disgruntled and overworked employees, or all of these things working together. I don't have a good solution to that, other than pax-facing employees being reminded to stay ahead of potential problems. And that also means that the airline has to do its best to not create problems that only get resolved in an ugly way at the boarding gate or on the aircraft.