"To defend your person, you need a hand gun. To defend your home, you need a carbine or a shotgun. To defend your liberty, you need a battle rifle!" Sounds right to me. (I live in Colorado, a "castle doctrine" (Leftist) state. That basically means that you can't use deadly force on anyone... regardless of how threatening your perception, unless they are encroaching upon your domicile". That means... if some douche is on your front porch with a gun in his hand, you can't take action against him until he breaks down your door. (How's THAT for a Lefty concept?) At the gun club they say... "if you shoot someone on your front porch, be sure to drag him into the house before the police arrive".)
As for the good guy with a gun vs. bad guy with a gun argument: https://vpc.org/revealing-the-impacts-of-gun-violence/self-defense-gun-use/ In 2017, the FBI reports there were only 298 justifiable homicides involving a private citizen using a firearm. That same year, there were 10,380 criminal gun homicides. Guns were used in 35 criminal homicides for every justifiable homicide. Considering 40% of households hold guns these are pretty bleak numbers for using it as a defense mechanism. Another interesting fact is that there were 486 accidental firearm deaths that year. So you're more likely to kill yourself accidentally then a criminal.
Regarding, legal Gun carriers: Every state restricts how a conceal carry or open carry individual can use his or her firearm. Since I do not have a permit to carry a firearm I cannot provide an explanation as to why a person or persons in my specific area would not use his or her firearm to save an individual, but I do know the whole purpose of having a conceal carry or open carry is for self protection,
To defend your liberty from an oppressive government you need a tank. Nuclear weapons would be helpful too.
In some states you can use your weapon to "defend someone other than yourself". In other states you might face prosecution for doing the same.
As a private citizen you're more likely to accidentally kill yourself then to perform a justifiable homicide: https://www.statista.com/statistics/251894/number-of-justifiable-homicides-in-the-us/ https://injepijournal.biomedcentral.com/articles/10.1186/s40621-019-0220-0