Because your armchair quarterback method of criminal analysis is only displaying your ignorance for all of us to witness. Regardless of how his arm was caught, of which there are many ways, the suspect was trying to elude the officer and his commands to STOP. You lose a few "rights", as you refer to them, in those circumstances. Intentionally dragging a police officer with your car while eluding arrest is considered deadly force and endangered that officers life.

Consider the suspect lucky that the officer didn't raise his firearm to discharge it at the victim as he had every "RIGHT" to do!

Now...go back to your popcorn and soaps...