You can expect law enforcement to be 'perfectly rational and fair', but expecting them to always be gentle is unrealistic. When people are being violent, it sometimes requires physical force to restrain them, and oftentimes that physical force can't be gentle.
In addition, being 'perfectly rational' does not always mean doing the correct thing every time, with the benefit of hindsight. You can be rational, but in real life we have imperfect information. Innocent people are sometimes hurt because of this imperfect information, even if everyone behaves rationally. It sucks, but is unavoidable.