I'm finding it more and more difficult to picture wide spread societal breakdown to the point ravening bands of looters would be roaming the suburbs and you'd need prolonged 24/7 over watch. Well, barring a pandemic or meteor strike etc. It seems to me that even in the event of currency collapses in Argentina or the Weimar things were not at that level. Unless one envisions a return to the literal dark ages where men forget how all that fancy technology stuff worked (and lost the ability to decipher the texts describing it) then having 50k rounds of ammunition seems to be a bit impractical. Especially if other items (food creation, medical care, ability to actually use all that equipment etc) is neglected. Not being negative towards anyone who does see that as a strong possibility, just my own viewpoint these days.
Your viewpoint isn't at all unreasonable. The odds are mainly in favor of "tough times" rather than total SHTF. As Micro's pointed out, Rome survived as an Empire for several centuries longer after the Republic had fallen. Barring an asteroid or WWIII, I'd lay money on a "at least the trains run on time" sort of American future, maybe up until the ages of anyone on this board's great-grandchildren.
And plenty of modern "first world" nations have and are faring worse than what we've got going on right now, without America's massive economic "momentum" (or land, agriculture, or resources) for lack of a better term. Nobody is expecting Greece to look like "Mad Max" or even Sarajevo, even if there's total default and a withdrawing from the Eurozone over there.
Although OTOH, according to Ferfal's blog and articles on these events, armed gangs going house to house DID happen to some degree, way above the "normal crime background rate" for Argentina. Bad enough that most folks needed (but did not have) a LCMSR and fortified doorways. He also pointed out that the rural folks generally fared worse in these attacks, since the looters could occupy the home for a few days/weeks, and er... "play" with the occupants with little chance of being heard. Playing the odds, row houses in a good middle class neighborhood was actually your best bet, since your neighbors, and potential help was often just a wall away. If the family did get wiped out, at least it was quicker.
And in places like SA, as I'm sure Jocasee can tell you, razor wire and security gates inside one's own home are commonplace.