Typical, it's everyone elses fault bar the person responsible in the first place.

The message should be "if you're stopped for any reason, be polite and respectful, if you're detained, be compliant."

You can be "detained" without being arrested. Detained means you're held while the facts of the matter are ascertained. You may be released or arrested once those facts are determined.

If you brandish weapons, you should be prepared to suffer the consequences.

As I mentioned, cops have been killed or severely injured by people who wouldn't comply so if you've brandished a weapon or made "sudden movements" when told to keep still, in the heat of the moment it's no wonder a cop uses far more force than appears necessary with the benefit of hindsight.