That's basically a complete misunderstanding of what happened in Sweden. You've put the cart before the horse, in describing what Sweden chose to do. And I'll reiterate that point, chose to do. They thought about it at a national level, considered all of the resources they had, and made a number of choices about how to use those resources. They didn't start with "herd immunity." That was an after thought. First they decided to focus their national resources on the most vulnerable population, seniors ... which blew up in their faces later when the 'herd' started to show up at the hospitals and overwhelmed them. .
"Herd immunity" was a symptom of that focus of resources. This is all we have left, so we'll have to rely on voluntary compliance by the population at large. As much as anything the choice of "herd immunity" in Sweden was a vote of confidence by health officials and politicians in the general Swedish population's ability to think beyond individuality, and accept responsibility for other peoples' health and the public good.