You really are naive to the point of being completely without anything resembling intelligence. Tell us, in the event of a catastrophic collapse in which cities are left without resupply, when things are at that level of disruption, how, exactly are the soldiers in Iraq and Afghanistan supposed to get themselves home in order to support your murderous roving packs? Second, what makes you think they ARE going to support the government (assuming the government is still running things)? Those in the military tend to take my view of preparations, not yours. There will be those willing to accept and act on illegal orders, but there will also be those who will not - and the two factions will probably end up fighting each other as society continues to collapse around them.
And you REALLY think the roving bands are going to be even remotely civilized? "gather the people together" LOL Do you really think, once people in the cities realize there are no more trucks delivering food to the stores, they will cooperate with each other and other roving bands "for the good of the nation"? Do you really see starving people asking law enforcement for help and following their instructions, allowing law enforcement to take away what they may have managed to gather for themselves to give to others who were not as successful in finding food? Do you really think people will be satisfied with their "fair share" if that "fair share" is not enough to keep them from starving to death? If so, your naivete is actually worse than your love of mommy government. If people are not getting enough to eat who are USED to getting plenty, they will do whatever they can to get as much as they can, including turning on each other. No one is going to stand for government taking subsistence level supplies away from them so that more people can have less-than-subsistence supplies. You want reality, people will be turning on each other, killing for what the other has, long before they have the time to notice a particular house looks like a good place to raid. And when said house sends a few of them to the pavement, the rest are far more likely to continue to prey on each other than try to force themselves on a known lethal area. People take the path of least resistance - and that path is preying on others who are not armed. By the time people become desperate enough to consider attacking a known defended hold, they are likely to be too weak to be a threat anyway.
The bottom line, IF the worst happens and cities lose the ability to be resupplied, people will be looking for enough food to get them to the next day, and they will not give a ripe pig fart for the continued existence of government - INCLUDING law enforcement. You really are an ignorant droon. The absurdity of your description of the way things could/should happen post disaster would be funny if your support of a totalitarianism in government were not so dangerous.
And the role of government, as defined in the Declaration of Independence, is to protect the rights of the people - NOT to protect itself at the expense of peoples' rights.
THAT is the role of our government. A totalitarian government puts itself above the people, places the existence of the state above the rights of the people. A government of free people does not - and in that strength will be more likely to survive where a totalitarian government will not.
But it has been apparent for a long time that you love the idea of totalitarianism, so your precious mommy government can hold your hand, feed you with your little spoon, tuck you in at night, read you a nice bedtime story from your collection of Dr. Seuss, and make all your decisions for you so you don't have to worry about anything resembling personal responsibility.
BTW: it does not matter if there is plenty of food. If transportation breaks down, cities will be without food no matter how much in in the granaries and warehouses out in the country. Also, if transportation breaks down, people will be on foot for the same reasons the trucks aren't running. Food storage tends to be where the majority of food is grown, which in turn tends to be a hundred miles and more from high urban areas. How many miles do you think you can make in a day, weakened from hunger and possibly (probably?) sick from drinking unclean water? How many people do you think will actually make it to the rural food stores, guarded or not? Of those, how many will have the strength left to forcibly take it from those who are guarding them?
Now I would hope that people in charge of granaries would have some system set up to provide for those refugees who make their way out of the cities. Large granaries and food processing warehouses do have enough food to share, within reasonable bounds. The self- limiting actions of refugees from large urban areas would probably assure those who make it to the stores will be few enough to not overwhelm the stores.
However, if a family has a few months of food stored up, and the disaster looks to make it unlikely they can attain more before they are likely to start running out, then I would NOT expect those people to put their own children in danger of starving in order to feed others. A parents' FIRST responsibility is to their children, period. NOT to government, nor society, nor even community, unless such INCREASES their chance of survival. Feeding refugees from limited stores DECREASES the chance of survival. An individual may make such a choice. A parent (or grandparent) would be remiss in their primary responsibility to make that choice.