>If you rent a car and it doesn't work, would you pay for it?
The rental car company has a fleet of cars, and they will put you in one that works. It happens, cars have many moving parts and they are known to break down - the rental company knows this and will replace the car in almost all cases. Nobody is paying for something that doesn't work, but the rental company pays to get the broken car fixed, which is part of their cost of doing business.
>If you rent an apartment and its unfit for habitation, would you pay for it?
There are laws about that, for very good reason. Nobody is forcing anyone to live in squalor, though it sometimes comes down to poor people not having money and living in bad situations. People absolutely can and have sued bad landlords, and the city steps in if the people speak up. I know I've had to get the city called out to address a situation before, and the landlord paid to make it right.
>If you go to the store to buy a product and it's not there, would you pay for it?
Come on now, this is getting ridiculous. This is a non-issue. If you pay for a product and don't receive it, then that's fraud and at worst you can sue to get your money back. Usually you just get your money back.
>Why should the employer pay for work that isn't being done?
This is much like the rental car in that the employer has to pay to keep the employees healthy. They employ people to do the work, and they need to be hired, on-boarded, trained, and gain experience in the role. People aren't like cars and can't be replaced as easily. The employer should understand this and much like the rental car company keeps a fleet of cars, the employer with more than 1 employee has them for continuity of business, and paying them while sick is part of what ensures they won't need to seek a different job that will pay them while sick. It helps retain a trained and dedicated worker. It's the cost of doing business. Or, the business can suffer and be understaffed because the employer didn't account for humans ever getting sick (which humans are known to do pretty often), so if the business wants to cut corners and not pay people, then they will end up being understaffed and their business will suffer. This is really basic business stuff.