After taking the money, the robber ordered the manager into the front walk-in cooler and shot him to death.People talk about how cooperation with violent criminals will turn them non-violent, at least for the duration of your transaction. The truth is a bit uglier. Criminals don't like witnesses. Dead men tell no tales.
Being prepared to defend yourself does not mean you will be able to defend yourself. Being prepared for a car crash (by wearing your seat belt) does not guarantee you will survive every car crash. But you wear seat belts, don't you?
Cooperating with criminals is not the solution. Just take a look at what is going on off the coast of Somalia. "If you give a mouse a cookie, he's gonna want a glass of milk."