Let me chime in...that's not a dumb question, but logically coming from a view of you and I both living in so-cal its not that practical to use for home defense, reason being..as mentioned it can go through walls, even your neighbors wall. I know several people that live in o.c with ar15's that use it for sport shooting it's a good weapon for medium range.
I doubt in so-cal we have to worry about katrina, but think about a large earthquake...it would be katrina like, a riot...yes that is in the possibility. As for home protection, look at Yellow nsx's post...a shot gun would get a great choice, you can buy shells that do not penetrate wall's but he has a higher end one which is semi automatic...a pump one would be fine, once an intruder hears the "shuck, shuck" of a pump they will be most likely to flee. Downside to a shotgun is that it is hard to conceal in the house do to the size. I personally use a Sig 229 for home protection, there have been instances where I did awake to weird noises and had to grab it...luckily a false alarm...I recommend having a gun, before its too late.