I'm sorry for posting this here, but is the natural progression and no one is responding in that other thread. I guess it is my turn to troll?
Heroin is more easily produced and smuggled than guns are, so it would be quite easy to grow it within the US or, as is done now, smuggle it across the border.
Guns, on the other hand, can not easily be made or smuggled into the country from non-North American sources. Accordingly, most of the guns available to thieves are black-market from robberies or legally purchased. It stands to reason, then, that lowering the number of guns available within the US should decrease the number of guns available to criminals specifically.
As an example, here in Canada we are far more restrictive on what guns you can and can't have. Our crime rates, and specifically our murder rates and murder by firearm rates, are substantially lower here than both Mexico and the US (who have more relaxed laws). The problem we have is with guns smuggled into Canada from the US because of the lax laws at the border and within the US; the same problem does not exist going from the US to Mexico because the penalties for bringing even ammunition into the US is up to 5 years in jail.
Now there is no way that I can make a direct correlation between the stringency of gun laws and the crime rates, and neither can any of the pro-gun folks. Studies of the effect thus far are generally inconclusive or contradictory to other studies. I'm not against the possession of guns, but I do question the argument that wide-spread gun possession directly leads to lower violence, or somehow makes everyone more safe.
Sure, but the point is to make it extremely difficult for them to do so.