If you are mad at somebody at work and you hit them a little bit that is egregious and completely unacceptable behavior that should end your career and is an actual crime. Even just hitting somebody a little bit is wildly off base for ordinary and healthy human interaction when angry.
Beating somebody to death is many levels of escalation beyond that. You don't need a superior to tell you not to do that. I am extremely confident that there will be exactly zero situations in my entire life where I am so angry at somebody that I even want to beat them this badly, let alone actually act on it.
This is about police institutionally seeing the populace as inhuman worms who deserve to suffer. This is not about emotions running wild.