I agree with the gist of what you're saying and think the question might then be a case of how far from the larger urban centers one might need to go to avoid the main centers of gang recruitment or looters, as well as finding that mix of community where you'd like to live that also provides the necessary amenities to survive. Even many urban centers might be alright, but I suspect that with economic and cultural changes, any location can change significantly even within less than a generation (Compare the 1970s vs 2003 blackout in New York).
Will the imagined gangs venture very far from their operating base? I appreciate the shortcomings of a static defence, but if a community can alert and assemble a sizable quick response force of citizens/police (i.e. a couple dozen or larger) there's a point at which the so called gangs would have to organize a stricking force of battalion size just to ensure victory. Without the compulsion of the state, or in the original scenario any underlying cause, how well effectively can such groups be built up and maintained, and how far will they venture to seek out victims?
Those are great questions. If we're to assume these guys are motorized, as was the context of the orginal post, they've got considerably greater range than a foot-mobile mob, and can cover said distance quickly. I think the distance a city-based gang could strike into the country would be a function of a lot of things. It's a funcion of the availablity of fuel more than anything, as a motorized army marches on its gas tank even more than it marches on its stomach.
One thing to keep in mind is that oil refineries and pipeline terminals are typically in urban areas, not in the country. If thse guys figure that out and start staging raids for gas at the source, they're not going to have as big of a problem getting out into the country as conventional thinking might dictate. It all depends on how sophisticated their leadership becomes, and how long they are able to develop and mature.
I have been trumpeting the imortance of not underestimating the potential of the city folk since I came into this forum. One thing that is absent a lot of the predictions about the so-called "sheeple" is what they would be capable of under competent leadership.
That leadership will emerge. There will be perverse minds who take the things they learned as officers in the army or even n the prepper community and turn it to their personal gain. They will be more than capable of organizing people who are desperate and will do anything into a competent army of professional troops. I've met officers in the army during my career who I would consider capable of that kind of thing - and who would be more than capable of pullling it off. Furthermore, there is firm historic precedent for this kind of thing going down, all over the world at all times in history.
Thinking that everyone with the skills to survive will simply use them to survive and will mind their own business and dothe right thing is probably a flaw, perhaps a fatal one.
As much as we like to profess total self reliance, the reality is that because of the problem state in this thread - the post-SHTF emergence of organized, proficient, thugs - homesteading successfully depends on a fairly rapid return of a friendly government capable of maintaining order in the cities and preventing gangs like this from forming, and the more time goes by, and the more proficient those gangs become, and the more sophisticated their leadership becomes, the bigger the problem they will pose. It is a threat that will grow over time, not shrink. Their range will increase, not decrease.
Having a QRF consisting of local cops and citizens will work for a little while but the reality is that you will always be on the defensive in this situation, reactng when they show up and trying to drive them off. If there is no one to pursue them and deal with them on their own turf, then you're always fighting at home, which is also not a sustainable situation. They can retreat; you can't really do that, so all it takes is once loss in battle, just one time, and your combat power is reduced to zero.
And that failling, if they just want to pee in your campfire for the sake of spite, they can ride by on the ATV's throwing firebombs and burn all of your crops, buildings, cattle, etc. to ashes. Then your sustainable source of food isn't really producing for you.
Your survival as homesteaders depends on someone being at the wheel of government larger than your community, because your community does not have the assets -intelligence, mobility, combat power, and so on to engage the enemy described in the original post. Plain as that.