>Why does a price necessarily include a profit or a loss
It includes a profit or a loss because you need to eat and provide for yourself. If you're making chairs but the cost of materials is larger than what you sell those chairs for, how are you going to provide for your family? If you want to save up for a house or a car, or family vacation, how are you going to do that if you don't sell your chairs with a surplus (i.e. a profit)? A market-based system necessarily implies a profit motive.
> If you're making chairs but the cost of materials is larger than what you sell those chairs for, how are you going to provide for your family?
This is the "self-referential" thing I was referring to. You're entering into this thought experiment with a pre-defined conception of how an economic mode of production must operate. You're presupposing the profit motive.
It includes a profit or a loss because you need to eat and provide for yourself. If you're making chairs but the cost of materials is larger than what you sell those chairs for, how are you going to provide for your family? If you want to save up for a house or a car, or family vacation, how are you going to do that if you don't sell your chairs with a surplus (i.e. a profit)? A market-based system necessarily implies a profit motive.