, the right of the people to keep and bear arms shall not be infringed.
In the tumult of 18th century politics, the men who ratified these sentiments understood that disarmed citizens were more easily cowed by an ambitious sovereign. They held that the weed of tyranny quicker chokes the garden of liberty when the gardeners have been stripped of the, uh... trowels of, uh... revolution, I guess.
Failed metaphors aside, the economics are straightforward. Armed citizens are marginally better able to kill than unarmed citizens.
I of course use "kill" here in a neutral sense. A hunk of fabricated metal has no sense of justice. A pistol in the hands of a street thug will perform the same function as a pistol in the hands of a taxpaying homeowner. A service revolver in the hands of a rightfully appointed deputy of the law will take a life as surely as a service revolver in the hands of a corrupt cop. A rifle in the hands of a dutiful Soldier defending the homeland against foreign aggressors kills the enemy as surely as a rifle in the hands of his counterpart on the other side of the firing line.
But as gun control proponents rightly point out, the right of the people to keep and bear arms is far from uncircumscribed. Why is it that the logic of prohibition does not apply to polonium or cyanide or white phosphorous or Claymore mines or Anthrax or uranium-235 or mustard gas? I reckon there's a bit of a black market in these things, but atropa belladonna is more likely to show up as part of a show garden than as the lethal poison that earned it the nickname of deadly nightshade. What's the difference? Why do drug cartels arm themselves with AK-47s rather than sarin gas? Why isn't there a more robust underground economy in the relatively easy-to-produce phosgene? If you're looking to kill, a corpse is a corpse regardless of whether it's riddled with bullets, dissolved in acid, or suffocated in gas. The economical approach is to maximize benefits while minimizing costs, yes? Law-abiding citizens have sensibly prohibited the use of indiscriminate weapons of death, and of poisons. Surprisingly, criminals have largely agreed. The ban on chemical, biological, and nuclear weapons is mostly effective! Why?
Some of it is probably because of ordinary persuasion. It's cowardly to poison someone; it always has been. Yet it isn't cowardly to shoot someone, even (evidently) from thousands of miles away in a metal box stuffed with electronics. Guns are honorable—more honorable than poison, anyway. Poison is dishonorable. Gun rights folks are keen enough to recognize that the logic of prohibition would apply to firearms: the bumper sticker version runs "if guns are outlawed, only outlaws will have guns," so imagine how great it would be if those same folks understood that the same precise line of thinking applies to narcotics.
In the case of banned agents of death, what the legislation has done is to encode the law. There's pretty much wide agreement that combat toxic agents have no legitimate place in a civilized world. There is substantial and meaningful disagreement about a similar role for recreational drugs and firearms. The disruption to the orderliness of civil society and the increased state-led oppression that accompanies the ban on the drug trade means that the voluntary exchange of narcotics would be more euvoluntary but for the statutes prohibiting their trade.
How is heroin not like aconitine? The power of rhetoric. Bans carry unintended consequences. Persuasion works exactly as it says on the tin.