One obvious interpretation is that right to carry laws cause lower murder rates. I'm skeptical of this interpretation because it's hard to conjure up a realistic theory of how this might be happening. One popular theory is that in a world where everyone has a gun, they're all too afraid to use it. Fear that the victim might have a gun discourages the crime ever taking place. This is probably true sometimes, but I just don't think that the typical American is so old-west that they'll pull out their gun to put a criminal in his place. "Don't be a hero" is a more realistic policy for almost everyone, and probably a better one anyway.
What I notice with each graph is the murder rate dipping before the right-to-carry laws are ever enacted. This indicates that perhaps in places where murder rates are already falling, people feel safe enough to support right-to-carry laws.
I like this interpretation, but I see two problems with it. One is that murder rate within each state seems to decline faster than national rates. Two is that it depends on the population having a clue about what the murder rate even is. And we know how little the population knows about national statistics. If you ask them, the murder rate is always at an all-time high.
Which leaves me at a point where I may have to rethink the whole thing. Out of the forty states where "Shall Issue" right-to-carry laws are enacted, we have graphs for three. Perhaps what we see here is not typical.
I recommend Scott Alexanders post about Guns and States, where he has insights such as these:
The United States’ homicide rate of 3.8 is clearly higher than that of eg France (1.0), Germany (0.8), Australia (1.1), or Canada (1.4). However, as per the FBI, only 11,208 of our 16,121 murders were committed with firearms, eg 69%. By my calculations, that means our nonfirearm murder rate is 1.2. In other words, our non-firearm homicide rate alone is higher than France, Germany, and Australia’s total homicide rate. Nor does this mean that if we banned all guns we would go down to 1.2 – there is likely a substitution effect where some murderers are intent on murdering and would prefer to use convenient firearms but will switch to other methods if they have to. 1.2 should be considered an absolute lower bound. And it is still higher than the countries we want to compare ourselves to.and,
On the other hand, lives are very valuable. In fact, the statistical value of a human life in the First World – ie the value that groups use to decide whether various life-saving interventions are worth it or not – is $7.4 million. That means that gun control would “save” $22 billion dollars a year. Americans buy about 20 million guns per year (really)! If we were to tax guns to cover the “externality” of gun homicides preventable by Australia-level gun control, we would have to slap a $1000 tax on each gun sold. While I have no doubt that some people, probably including our arsenal collector above, would be willing to pay that, my guess is that most people would not. This suggests that most people probably do not enjoy guns enough to justify keeping them around despite their costs.