An armed intruder being able to commit a crime and leave before police arrive is absolutly plausible, and in fact, happens all the time. 1/2 of all murders in San Francisco, for example, remain unsolved.
I would like to be one of the few who don't need to rely on the police to protect the lives of myself and my family.
I am more concerned with this scenario than the government marching into my home with a gun confiscation order. And, even if they did, I know a place to buy a gun for $200.00 without the waiting period. :) Free men do not ask permission to bear arms.