It’s not gonna stop the entire armed forces. But it might hold back a rogue cop or right-wing vigilante from committing some atrocity. Besides, the 2A protects not just so-called assault rifles, but also less-scary-looking rifles, pistols, knives, brass knuckles, shotguns, rocket launchers, grenades, etc. It’s never been about an either-or of “guns make us free or we are disarmed slaves” … it’s always been that the better-armed the oppressed classes, the more they have been able to maintain their freedom in the constant push-pull struggle against the exploiting classes.
Agreed that the 2A needs to be updated for the changing times. Suggested replacement text (draft): “No person, aged 18 years or older, residing within the United States, shall be required to surrender firearms or weapons capable of causing comparable harm, unless such sentence be imposed directly by a jury of that person’s peers upon conviction of a statutory felony by due process in a lawfully constituted tribunal; nor shall any such person be penalized for the possession or lawful use of weapons of this sort. No amendment to this Constitution, or other law, purporting to repeal or modify this article shall have force of law.”