Ok so because the clerk behind the counter is someone elses loved one it is of no concern to you? interesting.
so if your certified in CPR and someone is choking....? thats no concern of yours either?
Bad analogy.
1. When performing CPR, you are absolved of any legal liability if things go badly. It's a LOT fuzzier if you shoot someone.
2. If CPR or Heimlich is needed, the worst-case scenario is the same as the result of doing nothing. In the robbery example, there is a wide range of possible outcomes, some better, some worse.