The idea here is that high risk people take extreme precautions. It's not an argument I'm making but it's one I understand. So if you have contact with a high risk person you should also take elevated precautions. So yeah, it's not any more simple or complicated than it is.It's not that simple. Because those people themselves interact with other people, some of whom have not signed up for that risk. For example, a person with compromised immune system might never leave their home but might live with someone else who is an essential worker or depend on someone else for their groceries and medicine. Those people depend on the community wide spread to be low to lower their personal risk.
Life involves risk. It always has. We're all going to die.
During a pandemic we should all take special precautions.