Robin, we’ve existed for over 200 years without anything even slightly resembling the tyranny you fear. England the same. Australia the same. In Germany the genocide was immensely popular and the few who opposed it would have had zero chance of stopping it. In fact such guns possessed by their neighbors would have quickly ended them.
All this is to say that your fears are extremely unreasonable. They’re equivalent to walking around wearing a lightning rod on your head on the off chance that some day you might be struck by lightning. But that would only injure you so you could do that if you want.
But when these irrational, paranoid, ridiculous fears of mass invasion or minority engineered totalitarian government of a country with over a 200 year tradition and culture of democratic government cause material, daily danger to innocent citizens, then that irrational fear and paranoia has got to stop being the cause and excuse for that harmful conduct.
At some point irrational, unreasonable fears have to yield to common sense.