I think people forget whilst they are themselves fit and in a low-risk category, they will still get ill just probably not severely, and importantly will be a carrier to spread the virus to others. To near-family, children, nieces & nephew and grandparents, or just to more at-risk people they meet on the bus, cafe, office, hospital, etc.

Or indirectly to other fit people who eventually down the line infects a high-risk person.

So I think it is quite selfish to expose yourself unnecessarily. I don't think we should stop everything we do, life still goes on, but just be considerate of others.