In the absence of firearms, the person who has the next most dangerous weapon can easily dominate everyone else. The country where I'm from was disarmed by the British to keep us from fighting them. But armed gangs still terrorize people with knives and machetes and whatnot.

Some fraction of the population in any society is antisocial. A non-zero rate of firearms ownership allows the people who aren't antisocial to suppress those who are antisocial and maintain peace.