Where I come from that 18 to 50 thing has a name: Draft.
Sentries, perimeter patrols? Patroling the community looking for what? "Suspicious" persons? Persons without valid ID?
Wouldn't that be very close to creating the kind of society we want to defend ourselves against?
Self defense as and when necessary, yes. But I think there should be a very high threshold for when patrols in the streets are considered necessary.
Nothing wrong with knowing how to shoot, though, just in case. And I can think of worse ways to spend a day than going to the range.
Edward, blunt objects are too nice. You should be tied to a chair in front of your computer with the volume turned way up.