I personally don't believe that attempting to float the idea of herd immunity as a viable option (sans a viable and effective vaccine) is helpful or responsible either, but perhaps that's just me. It's worth recognizing that relatively early-on based on the very limited information a case could have been made for it. Based on how most countries reacted it was not a compelling case, but not a Flat-Earth situation either. From a news story today https://www.yahoo.com/news/parents-knowingly-sent-kids-coronavirus-170052665.html “The human behavior aspect of sending sick and positive children to school is not something we can control, and we never accounted for people completely disregarding basic health guidance,” Johnson said. “We have no tools left, and we just want everyone to be safe.” As much as I suggested caution above, any plan that didn't account for parents sending sick kids to school wasn't developed by anyone with normal school experience. There are any number of reasons it should have been easy to imagine parents sending kids anyway. A little cynicism about human behavior and rule breaking is useful when trying to make plans.