If you were a criminal and wished to perpetrate a crime - would you choose
an area where you were very certain law-abiding citizens had no way to
protect themselves, or an area where you were likely to end up on the
receiving end of justified defense?

What on earth makes you think that criminals somehow pick and choose where
they are going to commit a crime? Most of them don't have a whole array of
transportation options. They more or less have to commit their offenses
within walking distance of wherever they wake up in the morning. They don't
consult the internet, the census bureau, or even the World Almanac to
analyze handgun ownership patterns across various zip codes. Based on
interviews with offenders, it rather appears that most of them don't even
have any firm plan of committing an offense until maybe 10 seconds before
they actually do it, and they simply aren't bright enough to weigh all the
costs and benefits in those 10 seconds. Most of them wouldn't be able to
form a coherent thought if you gave them 10 hours.

I agree that, for you and -- both reasonable people -- it makes sense to
avoid areas that are well protected by an armed citizenry. But the guy who
is desperately looking for $20 to get his next blast isn't all that
reasonable, and will go for the next open window he sees. If he had the
ability to think about things, he would be concerned with the pressence or
absence of an armed homeowner. But he isn't thinking about that, and
nothing is going to make him think about it.