You don't have to make it impossible to break into your shelter, just harder than getting access to someone else's resources. It's the same as the door locks on my home. I have picked my door locks (kids - oops), but I still lock my doors when I'm gone. Most criminals are lazy and would rather walk through an unlocked door than learn a real skill like picking locks. A series of assaults by other survivors? Not likely. Most zombies would rather go after urban apartment dwellers than try metal detectors to search for a bunker, or use explosives to break through reinforced concrete. Note: I don't have a bunker, but I think their value is being dismissed based on an inappropriate comparison.
As for surviving after SHTF, I feel sorry for those who would give up like this author implies. I intend to survive with my family, and I expect many friends in my area to survive too. Life is a beautiful gift from God, and I have no interest in throwing it away until He chooses to take it back.