The worst effects of a crime are directed against a single person--you mug or murder a human being, not a plot of land.

I'd add a caveat that many of the side effects of crimes are area dependent--a gunshot will disturb and affect the psychological wellbeing of far more people in very dense areas. That's why many people end up with an overstated impression on how common crime in cities is.

Though I think even per capita, most cities have it worse than the suburbs...