People will form informal militias or they will submit. Being armed makes the first choice possible. Not being armed makes submission the default.
I agree with some of what you say, but I personally have always assumed that the veneer of civilization can be ruptured more easily than many of us imagine.
Beyond that, I actually disagree with your premise - I believe that mobs, rather than being enraged at a show of force, will more likely pass up armed targets in favor of other prey. And neighborhoods can band together too, making a much more intimidating show of force. That's what I imagine would happen, from necessity, if civilization begins to break down.
I agree, and that is generally a good thing, but I also think there is a concern for militias that are no better than thugs. Not everyone is noble and wants to save their family/neighborhood.
Power corrupts . . . It is not unlikely that when the SHTF some militias will prey on the less armed.
In 3rd world countries they are called warlords.