I believe that the original purposes included all of the above, but the founding fathers were thinking about muskets that held one projectile and took a minute or two to reload. Today, I think that hunting is a valid purpose, but the best guns for hunting are shotguns and rifles, not assault weapons. Self defense also seems valid today, but the preferred guns for that would be shotguns and handguns. Ensuring that the military has arms seems unrelated -- the military could have arms even if the Second Amendment was repealed. Protection against tyranny seems illogical. Even if a group of patriots had assault rifles, they would not stand a chance against tanks or helicopter gunships. I think that we need to move the line on what guns can be owned, and I would start with assault rifles. That said, I agree with those who talk about mental health. As we have seen, a truck can kill a lot of people in a short time, and a bomb can kill more. Humans have evolved as a species where part of our nature is to kill each other. We are to some extent the survivors of tribes who killed off other tribes. Overcoming that is a challenge, both on an individual level and a group level.