The homeowner who shoots an violent intruder isn't only defending his own home and family but also the homes and families of what would have been the intruder's future victims.
In response to a call for the restoration of the right of self defence in the United Kingdom, Glenn Reynolds wrote:
I agree. In fact, as self-defense against burglars generates positive exernalities, by reducing the number of burglars, and their willingness to break into homes which might be occupied (thus reducing the risk that people will suffer Mr. Symonds' fate), there's a good economic argument that it ought to be not simply tolerated, but actively encouraged and even subsidized.
The individuals who perform home invasion robberies and other violent crimes have chosen to act as though they were predatory animals. In doing so they have deprived us of all other options but to identify and deal with them as such.