Evil and insane people unfortunately do exist. Some of the failures of modern technology are directly related to refusing or ignoring this inconvenient truth.
Sadly, crime is fundamentally asymmetric: a small number of bad actors can inflict damage and pain on a large number of victims.
This is particularly well-known in the domain of public urban facilities, where everything can be assumed to suffer vandalism or sabotage at any given time. You only need a handful of thugs to have a “gang” that can effectively demolish anything fairly quickly, including facilities used by hundreds or thousands of people. Defensive design, in this domain, is not just warranted but necessary.
