Here's the flaw in your post besides the obvious Breitbart. You take a national sample where the murder rate was already going down on its own.
In the Stanford study they chose areas where RTC was introduced when it didn't exist before. Therefore one can obtain direct data on the effect of these carry laws.
Actually no you can't. What would be relevant would be an increase in crime by those who carry. Were they responsible for increasing crime or others without permits responsible. If both, then by what percent.
If one can concretely examine all data and synthesize enough properly then one can make a claim. As it stands, no.
Perhaps broadband speeds changed and that's responsible for crime?
"Just because" or "common sense" reveals no truths, but it might provide some insight for those who reach for conclusions without rigorous scientific examination as to cause and effect.