Taking data from two different sources with completely different methods of obtaining their data is inherently unreliable, especially when one has a bias towards undercounting and the other towards overcounting and moreover they don't compare incidents of equivalent severity. In short, the comparison you make relies upon junk statistics of the sort only a university social sciences professor could love.
I'm curious as to why you think that the Bureau of Justice Statistics is biased towards undercounting (I'm not saying that it isn't, just wondering why you think it is).
Even if the data has some inaccuracies (as does most of this sort), do you really believe that they're extreme enough to negate the considerable gap between the two bars on the chart, or to provide credence to Bedstuy's assertion that almost no firearms are used to prevent crime?
What does that graph show? I don't know what a DGU is. So, it's utterly meaningless.
And, that's not what I said. I think police deter some crime. I think security guards and prison guards deter some crime.
But, if we're talking about situations where a private citizen with a conceal carry permit fends off an mugger with a gun, shoots someone in self-defense, shoots someone to defend a family member or innocent third party, stops a robbery by pulling out a gun, etc, that's rare.
On top of that, when people have guns, they take risks they wouldn't otherwise. They pick fights with violent people. They approach "suspicious" black teens in their neighborhood. They go into an opposing gang's territory. Because, they have that security of where they can always pull out their gun. And, maybe there is a potential deterrence, if that person gets into a bad situation. But, maybe they wouldn't have needed the gun, if they didn't have the puffed up ego of a gun owner. Unfortunately, dumb, angry with guns tend to find reasons to whip them out.