An explosion in the number of people interested in carrying concealed weapons has occurred in recent years, due to the belief that a "good guy" with a gun can deter crime or violence. The facts simply do not support this notion. A recent study that analyzed data on number of concealed handgun licenses issued from 1998 to 2010 and arrests in every county in Florida, Michigan, Pennsylvania, and Texas found no significant effect of concealed carry laws and increases or changes in crime rates ...
Cherry-picked data is no data at all; the above quote is a non sequitor, because to doesn't really have anything to say about the value of "allowing" law abiding citizens to carry a concealed firearm.
It doesn't' matter whether anyone can find verifiable data that a CHL ("Concealed Handgun License", in my state) has had a "significant effect of concealed carry laws and increases or changes in crime rates"; what matters is that the 'good guys' may legitimately carry a gun to protect themselves, their loved ones, and their property.
In a way, I have some issues with the CHL system. I think that the 2nd Amendment already justifies carry of a defensive weapon, and the CHL system is redundant.
But it does have some value, in that a LEO meeting an armed citizen can easily separate the felon-with-a-gun from the honest citizen (one whose right to be armed has not been abrogated by a felony conviction, etc.)
On the other hand, when a LEO meets an armed person, it's a matter of moments before a background check can identify a convicted felon who is forbidden by law to carry.
While I resent having to "prove" my status as a non-felon, it does have value because when (for example) I am pulled over by a LEO for a minor traffic infringement, the officer knows before he gets out of his car that (a) I am probably armed, (b) I'm not likely to be a threat to him. As I'm forthcoming with my drivers license, insurance card and CHL license when he arrives at the window of my automobile,
This avoids the possible tragedy demonstrated by the Philandro Castille episode, where a CHL driver was shot by a cop when he reached for his CHL .. inside his jacket ... and the LEO thought he was reaching for a gun.
Cops aren't perfect; so you have to be.
Thus endeth the lesson/
Yes, I've already said all these things before; they bear repeating.