There are always people, especially if you talk about 'few survivors' who would like to kill you just for fun, or some other reason that's doesn't merit 'why' question.

There is no defence against them, except to remove the incentive for any population to harbor them.

By the way, I disagree that military ways are obsolete. Iraq situation (i believe that would be your example) is not a military fault. It is an illustration what happens when army (after winning the war) is invited to perform police (or any other non-related) functions.

I didn't say military ways, I said big guns and big batallions as a recipe for "victory". I agree there is an important role for military along the lines of Roosevelt's "speak softly and carry a big stick". But things have changed and "armies" don't line up with rifles for a slugfest anymore. They seek jobs in airports, hospitals, morgues and wait for the perfect moment.