I hate repeated arguments, I really do. You know damn well what I say to that because you and I have gone over this already:
By the time you notice a person who has symptoms, they've already spread the disease to God knows who and God knows how vulnerable they are. Almost all contagious diseases work that way, and quarantine has always been about locking down people who are spreading the disease, not just the people you can visibly notice are sick.
By the time you see a sick person, that's not the time to ask how you can prevent its spread - it's already spread!