Kill him quick enough, and he won't hurt a bit. More than enough wackos, that a few would never be missed...and it stops them cheaply and permanently.
Should start with the ones running the asylum.
On the other hand, “continuum of force” and all that.
When I see good cops being chained to their desks and sued because of undoubtedly righteous shoots, I hate to think what would happen to a citizen who shot somebody who was not yet clearly (that’s important— clearly) a threat to anyone’s personal safety.