So... not as a weapon, only for target practice in designated areas.
Wiley.
You seem to enjoy trying to create strawman arguments. Your original statement was that those items could not be owned whatsoever, so regardless of how you try to paint them as being relegated to target practice, uncommon, or otherwise ineffectual, you were wrong. Period.
That being said, you can still legally use them - even in self defense - in a majority of the states. So yes, if Lil Mojeal decides to try to rob someone at gunpoint in a grocery store parking lot, and a guy who legally owns an M2 drives up, he could legally use the weapon in several states, just like he could use his own concealed carry weapon. No, not all states (as the laws for self-defense and imminent danger have different definitions), but a majority of them. My state (Tennessee) is one of those states.
But, even with that being said, using any weapon in self-defense is a strawman argument in and of itself, as the right to bear arms was never about individual self-defense from criminals, but the preservation of liberty as it stems from an armed populace.