he tried to stop the robber/murderer too, he shot at the guy, if using lethal force doesn't constitute trying to stop a robber I don't know what does. That he failed does not render him liable for every bad act the criminal commits.
the underlined part is straight up scary, and puts the truth to your lie that any of this is about protecting the public. you would rather stop law abiding citizens rather than criminals. In your own words you are saying the government should be focused on punishing a law abiding citizen more than a criminal.
and if they were so terrible you would be able to explain why, instead of deflecting. in all of those cases, including this gun owner, they are hypothetically responsible for a danger to the public, and through their own actions lead to the public being less safe than they otherwise would be if they hadn't taken the specified action. You just don't want to admit it because it destroys your argument, and also puts you in the crosshairs of the very standard you want to unjustly create.
I keep saying it, until/unless you are willing to apply any gun control measure to all the other rights, you are proving that they are bad intentions and likely unconstitutional.