Until we have an effective prevention or cure, we have to reduce the chances of catching it, especially during the period where people are spreading it before they show symptoms. Since it spreads mostly from prolonged time breathing the same air, the point of lockdowns is preventing those situations from arising. Quarantining after you become symptomatic is too late and without legal weight too many people won’t avoid situations to stop community spread.

That matters because there are things that you have to do, and you don’t have a way to control other people’s decisions. Closing high-risk recreational activities means that someone can go shopping with less risk because the people near them weren’t hanging out at the bar the night before.