FWIW I don't think you sound callous at all. To clarify my response, the data I shared on mass shootings ("mass" being >3 people) is just meant to illustrate that the "good guy with a gun" scenario is very rare.

As another data point, a Harvard University analysis of a National Crime Victimization Survey concludes that people defended themselves with a gun in almost 0.9% of crimes from 2007–2011: https://www.sciencedirect.com/science/article/abs/pii/S00917...