Because it permits such nonsensical statements such as "France has more murders per year than London" (therefore London is safer by comparison QED).
When you can draw arbitrary borders, you can make the numbers mean whatever you want.
When you can draw arbitrary borders, you can make the numbers mean whatever you want.
https://en.wikipedia.org/wiki/List_of_United_States_cities_b...
And you'll see that Washington D.C. doesn't make the top ten for rates of any of the major violent crimes (murder, rape, etc.) nor for the "Total" violent crime.