Please refrain from hyperbolic postulations - such are beneath you. As I told you a long time ago, when someone is highly intelligent - as you are (and that is with no sarcasm) - using such arguments actually weakens your stance, for people expect better of you. When a highly intelligent person uses arguments that would be more expected of someone much younger or less intelligent, it makes the intelligent person seem disingenuous.
As to your argument, you can use a mortar more than once, and you can use a grenade for self-defense. and both of those can be carried and used by one man...and while a grenade is a single-use, so is almost any rifle from before the Civil War, if one didn't have extra ammo and gunpowder. You can use a block of C4 for self-defense if you know where the bad guys are coming from, given time to set it up. More importantly to modern times, you can use a drone with a firearm attached for self-defense, or a drone with an explosive attached. Such are already being used in Syria, you know...and it's only a matter of time until people are killed here stateside using drones in either of those two fashions.
But even if we (rightly IMO) dismiss all that, you already said that you believe that crew-served weapons should not be allowed. Problem is, the loader in that crew is NOT a requirement, but a "really nice to have". One man CAN carry and operate a light machine gun. It wouldn't be easy, but it can be done. So what's the limits? Who determines which shade of gray is too dark or too light? Times change, and so do interpretations by SCOTUS.