I'm kind of surprised to hear somebody in America think it's a likely enough thing to happen to be worth the obvious societal cost of the wide spread weapons.
Realistically, if they did come for you, how much use would your weapon be? Do you believe that it would mean the difference between your life and death, or just that you'd feel better going having been able to put up some defence? Several genocides have happened in neighbouring countries from where I live in living memory, and it isn't at all clear that having access to a weapon allowed anybody who was targeted to survive.
The cost in mass shootings (now nearly two per day in the US) is a real cost borne by society at large. Your cost is still only hypothetical, and of unclear value if the worst did happen.