My argument is not "how it ought to be", that's your argument. My argument is, this is how it is.
I do not believe that excessive violence should be allowed or over-looked, but I also do not think that "excessive violence", when talking about a light push/"kick" to a person who's mouthing off and not co-operating, needs to be punished by putting the cop in prison.
I believe that police officers should be allowed to make judgment calls regarding the use of physical force, to a degree which they believe to be necessary in order to get a situation under control. If they make a bad judgment call, they should be reprimanded. If these bad judgments continue to pile up, they should be fired. If the bad judgment call results in death or serious bodily injury, we can start talking about more serious repercussions such as prison.
That's how the police have operated, and should operate, as far as I'm concerned. They do not apply to the same standard as what would be applied to a citizen, because that would obviously be ludicrous, considering the amount of physical interactions they are forced to go through, as a nature of their jobs. "Excesses", from the average person's point of view, are bound to happen, when we are talking about people who repeat these scenarios on a daily basis for a number of years.