A cop is more abusive to his family than the average man is. To a man with a hammer, everything needs to be nailed. To a man who is paid to use violence, everything appears to have a violent solution.
The use of force spectrum proceeds upward: compliance, passive resistance, active resistance, nonlethal force, lethal force. The law allows cops to use the level above the level of offender resistance.
There are many times when the average man does not gain compliance from his family. Because he is just average, he is not given special rights. Cops are different though. “The law” allows them to use force. And so, the cop who hears “no” from his family is inclined to use violence as a first resort.
Life has its own set of rules. They aren’t always intuitive:
The most dangerous gun to a cop is his own (suicide).
The most dangerous threat to his family is himself (domestic violence).