The people killed at Kent State were not protesters, at whom the National Guard were not shooting anyway. They were bystanders near the bookstore. Shoot live ammo into the air, it does come down somewhere. If you happen to be under it, it's a bad day.
However, if we're actually going to revisit armed protest in the United States as a historical phenomenon, we'd have to go back to the very beginning. It really isn't a "new form of American protest", it's the oldest and original one.