Self defense has many aspects, as you mentioned, locking doors and alarm systems are a good start.
But a locked door does you little good when the intruder is inside, or you happen to be attacked while outside your domicile.
We look at crime prevention very similar to fire prevention.
Yes, you keep paper away from open flame, install smoke alarms and develop escape plans. You mentioned similar actions in relation to crime prevention.
But I prefer to own a fire extinguisher as well. After all, only a fool would believe that just because you have take some precautions and installed alarms, that a fire is now impossible.
Likewise with a firearm. It serves the same purpose as a fire extinguisher does with fire, it removes the threat and allows a defense until the appropriate government authority arrives.
Now imagine being on a board where people from other countries are telling you how they are prohibited from owning fire extingishers, and they feel safe because they have smoke alarms and fire departments. And that if a fire actually occured, they would attempt to physically confront the fire by stomping on it in order to buy time for their family to escape.
And you have some of them ( not you, deo gratias) stating that owning a fire extinguisher is a sign that you live in fear of fire, rather than how most rational people would view it; as taking steps to reduce the threat posed by the very small actual risk of a fire.