It's hard enough to train someone to leap into a conflict fast enough to prevent potential violence from being done, not to mention also expecting him to wait until the last possible millisecond before doing something.
You keep repeating this nonsense that he was responding as he was trained to, but the exact opposite is true. Cops are not trained to immediately choke and beat someone based solely on some person (a person who is initiating the disagreement and advocating hate and violence) says "this lady [who I am insulting and verbally attacking] is attacking me!" They are trained to intervene is such disputes and only use what force their own threat assessment indicated is warranted. Then they are trained to restrain the person as quickly as possible. Beating her is just the opposite of such restraining actions and if she were a threat would have put himself and other in danger. What the cop did was more akin to how an untrained street thug would beat a person to hurt them without regard for public safety.
Your conception of cops equates them to mindless attack dogs whose owner is every random person on the street barking orders to attack.
So you do admit that you don't care about the safety of the protestor. Not just cops, but humans in general are in most cases mindless dogs wandering around with everyone on the street able to order them about. I dare you some time to yell 'gun' in a panicked voice in a crowded theater and see what happens. Some things and instincts override the most rational parts of us and force our meat suits into action. Denial of this will serve nobody.
You are jumping straight to the defense, thereby acknowledging that the officer
did do something wrong, but was not in the state of mind to realize it.
Automatism (law).
Irresistible impulse. There's a reason it's a rarely used criminal defense. Also, the report the cop filed after the incident made no mention of a loss of control, which kind of invalidates the defense. Would you like to try again?