The point is 'tough luck' gets the entire office sick by making sick employees come in to work. You almost never want this. It has a tremendous negative effect on productivity.

You also can't ignore the psychological effect of having to 'give up' time off (for a vacation with your kids, or a visit to your parents on their deathbed) in order to avoid going to work sick. It causes people to go to work sick a lot more often, because they can't anticipate when they will need time off. It also diminishes the rate at which they will use vacation time because they can't accurately estimate how often they'll get sick.