Re: A gun is involved in every single mass shooting.
"" Join a militia first and show up every month for their meetings."
Because we really need militias, don't we(?)"
I think OP was referencing the US constitution where the right to bear arms is linked to the membership of local militias. I actually like that reasoning. There isn't (and won't be for a very long time) the political will in the US to amend the constitution re weapons. However actually enforcing the constitution with a stricter interpretation can have a positive effect on reducing shootings.
"A well regulated Militia being necessary to the security of a free State, the right of the people to keep and bear Arms shall not be infringed"
So if you're a regularly attending member of the militia, you can own and carry weapons in that context. Otherwise weapons have to be kept in locked cabinets at militia HQ.