Well, I'm talking specifically in terms of the concept of rational self-interest here. It's perfectly within reason for the workers to think they should be paid better, given that their labor is now worth more, and their interest of getting paid far outweighs the interest in a more profitable company. In the same way, it's perfectly within reason for the manager to attempt to maximize the company's profit, as it's in their best interest to do so, since a company that makes more profits will (theoretically, of course) pay the manager better. It's an obvious reason why workers have created unions since time immemorial, and the same reason why companies attempt to break unions. It's a complex web of relationships between who owns and manages capital and who works and ultimately generates that capital, and there are many positions one can take, such as the one you hold, or mine.

The workers are factually responsible for using up the inputs to produce the output. Imputing the positive and negative product, which together make up the whole product, to the employer is a denial of that basic fact. The whole product's value is the profit.

It is possible to have investment in capital and getting return on investment in an economy consisting exclusively of worker coops.

Not all anti-capitalists are communists