Do employers have the ethical right to create "make-work"?

Many years ago, I started work at a convenience store, working the midnight shift. The boss had a simple rule: you are never permitted to sit down. His philosophy was, he was paying for your time, and therefore he did not see that you had any right to sit down for any of that period.

One night, I had finished all my work: floors swept and mopped, shelves restocked and cans priced, drink machine cleaned, milk rotated, and so on. There was literally nothing left to do—so I decided to sit down. The boss (who was in the store supervising) told me I was not permitted to sit, that I must find something to do, since he was paying me for my time. I asked him what he wanted me to do, and he began listing tasks, all of which I had performed. When he couldn’t think of anything else, he ordered me to mop the floor. Again.

I refused. I had just mopped the floor, and doing so again was nothing but make-work. I was fired on the spot for insubordination.

Who was in the wrong?