I'm unsure how this would work in the US though. Everyone being on at-will employment, if you're sick you still have to go to work and spread the disease, otherwise your employer can fire you.
Most employers would rather you don't spread disease to everyone you come in contact with. It's pretty rare to find someone with zero sick days
Most software adjacent employers maybe. Service industry would rather have you sneezing into customer's food (as long as the health inspector isn't currently there) than have to reconfigure the schedule.
In California people are guaranteed 3 days. That’s not much when dealing with a flu-like illness. Additionally, it gives employers the right to cap the number accrued to 6 days.
My employer resets sick days to 0 at the beginning of the year, and you have to accrue them over time. I was sick very early in January and they were unhappy about it.