There is this belief that guns in more places will make you safer. The reason we are not safe is because of to many guns.
Leave the 2A out of this for a second. If tomorrow we could push a magic button and all guns in private citizens hands would disappear would we be more or less safe?
If all guns disappear we will be more safe.
On the other hand if that button magically gives everyone a gun we'll also be more safe from mass shooters. It won't stop the shootings but will significantly reduce casualties.
The downside to that is we will have more people shooting individuals due to conflicts and anger.
The easy way to counteract that would be to impose a death penalty for people who kill.