Physical violence is just about the last area we "need" laws because people really hate violence and will go well out of their way to avoid even the chance being subject to it. No matter how big you are you can't go around breaking noses without a good reason we all agree on because if you do that for very long a bunch of other people will gang up and break yours or worse.

To a first order, laws basically just codify how the government (the overwhelmingly dominant applicator of violence in any given society these days) will apply violence so that the peasants can reason about it in advance and avoid it.

You don't need any of that for the basic "if I do violence upon others without a damn good reason violence will be done upon me" workflow though.

So? Anyone with a badge can wreck your life with zero consequences, even if they're a pipsqueak. Many of these individuals absolutely hate being looked at the wrong way.