One of my employees wants to switch shifts and I'm not going to let them.
Is there a reason you are being inflexibe with them?
Because I'm at the top and I can decide how I want them to work
I think that's the wrong approach to leadership.  You need to try and be considerate when handling employee scheduling conflicts.  Otherwise, they might all quit on you.
It's a negotiation game. They can quit anytime they like.
They can quit anytime they like, but when word gets out that you're a bad boss then you will have a hard time hiring new people. Aren't you word about the cost of high employee turnover? I think your leadership approach is going to hurt you more than anyone in the long run.