You do have a point, up to a point.. every adult is responsible for their own health and safety, AND has a duty of care towards others. When you assume responsibility for managing others , you also assume responsibility for their H&S. Why because they are no longer free agents, They are required to carry out your lawful wishes. They cannot be expected to know the hazards , unless they have been warned and advised about them. How would the plumber you employ know that you have sacks of radioactive ore stored in your shed, or the electrician that you have flooded the cellar in co2?
Anybody employed in a position of supervisor,sargent, manager, employer needs to know this . Any company employing supervisors will run programmes on their HR responsibilities.
There is a legal term "duty of care " and it dates back a long time.