You've obviousely never fired a 223 weapon, had someone shoot 223 rounds at you or actually seen firsthand what a 223 does to the human body.
I own an AR15 currently and was in the service. I couldn't disagree with you more. Those firearms are designed for 1 thing and 1 thing only. No need for a citizen to have that much firepower.
if your definition of "firepower" is how many rounds you can carry, how many rounds fit in a magazine, or how fast you can discharge them, yeas, the 5.56 nato is a lot of "firepower"
if, like me, you count firepower in terms of killing the target with 1 shot regardless of range, firing through cover, and breaking shit, the 5.56 nato is weak sauce.
no responsible game hunter uses the .223 or even it's slightly more powerful twin the 5.56 nato to hunt deer. they dont put venison down reliably.
the 5.56 doesnt do much outside varmint hunting, as it lacks the mass to drop medium or large game, and is too energetic for use on small game (wabbits etc) since ragged chunks dont make for delicious.
the 5.56 is passable for man-killing but often requires multiple shots. as a weapon of military origin it does the job as designed. for suppressive fire, volume of fire and grievous wounding it works well. the doctrine at play emphasizes wounding over killing, since wounded enemies become prisoners easier, and wounded soldiers require 2 guys to haul them away for treatment.
there are much better rounds for serious business, but the description of 'temporary wound channels" and the myth of "hydrostatic shock" gives those who dont know any better the impression that the 5.56 has some magical power that makes it better than old reliable .30's and puts this wimpy round into the "high powered rifle" category.
nobody wants to get shot, and getting shot at isnt fun, but of all the available choices in centerfire rifle cartidges the 5.56 is one of the
least dangerous options for the target. light cover, and even household masonry walls defeat it easily. my .30/06 will plow right through bricks even at long range, because it really is serious business.
as aa citizen i find frequent need for the kind of firepower that makes the 5.56 look like a kid's toy. wild boar, elk, moose, and even deer are largely unconcerned by the 5.56 unless you get a perfect heart shot, but since the bullet is defelcted by shrubbery and light breezes thats pretty unlikely unless youre standing toe to toe.
and what of bears? even at point blank range, a .223 will only irritate a bear and make him hungry. mountain lions can stiull do a respecatble job of mauling you eating you and excreting you even if you shoot em with a .223.
your assumptions are based on your preconceptions, not fact.
Citizens need MORE firepower than soldiers, since the citizen rarely has an armed squad, air support and naval bombardment as backup.