It is very difficult to kill someone with narcan. Torture, yes. Kill, no. Important to have if you or someone around you is on therapeutic or recreational narcotics on a frequent basis, or if you are find yourself in an environment where you may tripper over someone who just OD'd. I don't carry it because the use case is so narrow. Plus if I care enough about them to jab them with narcan, I probably care enough about them to breath for them for a while until i can get some help.
My brother-in-law (appropriately) narcan'ed people on Central in Albuquerque twice. Nobody really seamed to appreciate it.
All good humans should carry narcan just in case.