The point is, people get raped. It's not a thing that can be totally prevented. You can reduce the risks of it, but like all crime, it's not possible to completely rule it out. You said it's like "what would you do if you shot yourself in the arm?", but it's more like "What would you do if you ACCIDENTALLY shot or stabbed yourself in the arm?" Since it's a thing that can happen, it's not crazy to ask what your response would be. To claim that you can 100% keep your wife from getting raped is to claim the status of a deity.
Does everything have to be spelled out for you?