Interesting article from Scientific American:
The claim that gun ownership stops crime is common in the U.S., and that belief drives laws that make it easy to own and keep firearms. But about 30 careful studies show more guns are linked to more crimes: murders, rapes, and others. Far less research shows that guns help. Interviews with people in heavily gun-owning towns show they are not as wedded to the crime defense idea as the gun lobby claims.
Although not a perfect analogy, I think of vigilante gun fantasies in the same way I think of people who violate the speed limit. I am sure that a few people will go faster than the allowed speed in order to do some good or to escape evil. It’s a big country! However, the vast, vast, vast majority of people simply speed for no justifiable purpose. It’s okay to talk about the do-gooder outliers, just as long as we acknowledge just that: they are outliers.