Are defense companies truly necessary in a stateless society?

I’m going to keep it short because my thought process is very simple: In a world where it’s understood that defense is a personal responsibility, everyone who would want the ability to violently defend themselves would own at least one gun and likely carry it daily. When that’s the case, on top of an already extremely gun dense nation, wouldn’t the only form of defense against organized violence necessary be defense of the home? What warlord or foreign power is willing to go door to door entering a hostile and dangerous situation in order to take sovereignty over an area? In addition, to do so would mean to massacre the very people they desire to rule over. So would an organized defensive militia be necessary at all?