I think its more the first line of defense, they are not there to kill, they are there to basically state I don't want you here without provoking a lethal response from whoever is encroaching on them. It causes a lot less death of their males since they are known that they are not a threat, reducing the overall attrition of them over time and making life easier on the hive. The females with the stingers come out if something is a real threat, ie something messes with the hive or queen.

Honestly, kinda reminds me of British (and other non-militarized) police. Don't send guns to every problem as most can be solved without it and some are made worse by their presence.