It's about accurately understanding the risk of different groups to make decisions about how to open up different segments of society, and to balance the benefits and harms of continued lockdown.
Under normal circumstances we don't throw everything at trying to prevent every death. So we could choose to fund the NHS and elderly care more, reduce speed limits, make vaccinations compulsory, outlaw smoking and alcohol, but we don't because as a society we balance the savings of lives against other priorities. So it is normal to have a discussion about how much we prioritise reducing deaths from covid19 vs the harms of those actions.
Under 45s with AND without underlying conditions have a very, very low risk of dying and hospital admission from covid19. The risk of death is very correlated with age, with male sex being the second most significant risk factor. Apart from the shielding conditions, most underlying conditions have only a small extra risk of death, so it's not that if you have asthma you will die from covid. Being male is more risky than most underlying conditions.
It seems crazy to keep kids out of full time education for an extended period of time when the risk to most children, parents and teachers is tiny. There are ways this can be worked to reduce (but not eliminate) the risk to the more vulnerable, predominantly older groups.
Alternatively if we choose to keep kids out of education for an extended period, that will have long-term harms too. If children grow up less educated, less socially and emotionally developed, that will have very grave harms for all of society in the future, so I don't think that is a decision to take lightly.
I like this blog on the subject of assessing risks around opening schools by a Public Health doctor:
blogs.bmj.com/bmj/2020/06/02/sebastian-walsh-we-are-asking-the-wrong-questions-about-easing-lockdown/?fbclid=IwAR0tddDArvQn4862FP-1Nb5XE59IVrUiidXMUZoDcpwhrckcApa2m6c106g