Pete
Where does this logic break down?
The break in logic occurs via the assumption that murder rates and other forms of violence are a single ingredient recipe. Criminologists have looked for a direct correlation between guns and violence and been unable to find it. A country, like the former Soviet Union for example, can have a gun ownership rate of effectively 0% and still have a murder rate of roughly twice what we have here in the U.S.
Mass shootings make me physically ill and it is tough to keep emotion out of the discussion. But the fact remains that an ordinary pump-action shotgun will put more lead into the air faster than a so-called, "Assault rifle" The term "Assault rifle" itself is one the Left coined to describe civilian variants of modern military rifles and as such, it is misleading and inaccurate. No military force on earth uses the AR family of rifle. It is not a battlefield weapon and never has been.
Personally, I would like to see the bar for gun ownership raised considerably. There's a saying here in my state to the effect that it's very easy to buy a gun here, but it's even easier to go to jail for a long, long time because of it. The laws regarding the carry and use of a firearm are quite complex and most gun owners are not versed nearly well enough.