Back to your issue of power&capacity/escalation of lethality: I (and others) already provided scenarios where there is a need for the public to have those.
I think this is where we disagree. My point is that there are many other firearms that could fill your perceived "need" in those scenarios.
I suspect our forefathers would be appalled at our skill with firearms. "Why do you need so many shots? Why do you need a scope?"
Keep in mind that the M-14 was designed to be accurate out to 800-1000 yards, but Vietnam showed soldiers didn't shoot the M-16 past 300-400 yards. You didn't "need" 7.62x51 when a 5.56x45 (or 7.62x39) was just as effective.