One constitutional change to the bill of rights would fix everything.
It would go something like this: "No unique right extends so far that its application causes material harm to the legitimate rights of others."
This is the tool of modification that justice and mercy each require and that seems to be missing.
Given this tool, would the second amendment continue to be sancrosanct, or would it gradually be drawn towards becoming merely reasonable? A person may be permitted a firearm, but other citizens may also be granted reasonable protections against them.