Why wouldn't herd immunity be an acceptable condition for the part of the population that aren't at risk to develop a severe condition? The balance is protectin

Why wouldn't herd immunity be an acceptable condition for the part of the population that aren't at risk to develop a severe condition? The balance is protecting those at risk all the while allowing those that aren't to continue working as normal. EDIT: I'm sorry, I misread. You're not against the idea, it just doesn't inform us as to how to balance our policies.