The 1950s were the reel golden age of science fiction movies. Consider the shots above from Attack of the 50 Foot Woman (1958). It is the story of a rich socialite turned into a giant woman by a giant alien. She seeks revenge on her cheating husband, something made easier by the fact that she is…50 feet tall. (She is also pretty sexy, wrapped in what looks like a few very big sheets, needed because her designer socialite clothes did not grow.)
The sheriff discovers that a pistol is no match for the giant alien, and as you can see, her husband learns that his pistol is useless against her. (She is ultimately stopped when the sheriff shoots an electric transmission tower she is standing next to.) This is an old story and a lesson we should have learned by now: pistols are not effective against aliens, monsters, people turned into monsters, etc.
Assault rifles may do no better, but at least they might give you a fighting chance and a little extra time to escape. The NRA, for some reason, has failed to make this argument. But it is both appealing and rational. The chances of the government turning against all its citizens may be small, but it could happen, and the NRA believes it and promotes the possibility. The chances of alien invasion, experiments gone rogue, the sudden appearance of strange new enemies may be small, but it could happen too.
In that case, would you rather be carrying a pistol, rifle, or shotgun, or do you want some serious firepower? You know the answer.