I don’t recall saying cops are useless. Are you sure you’re replying to the right person?
The police do illustrate over and over again that even trained professionals make bad decisions when issued guns. And of course the solution isn’t to escalate things by raising the threat of officers being shot, but instead in finding ways to have less people with guns, so police aren’t on alert all the time and aren’t as tempted to use their guns as their only solution.
As a thought experiment: If we gave every adult in the world access to fire the entire planet’s nuclear payload and destroy everyone, do you think we’d all be safer? Would the world even last 5 minutes?
The more people you give access to deadly weapons, the more likely you are going to run into someone who is stupid, impulsive, or downright crazy and is going to use that weapon to harm themselves or others.