That's because you're measuring 'worth' by income generated for the business. That's not how Marxists see it. If a business were to sell a product at a price below the marginal cost of labour, then you might have a point, but no business would do that except maybe for purposes of undercutting competition and monopolising the market.
A business also has other costs. In general, a business's aim is not just to "make a profit", but to make a specific amount of return on investment based on the riskiness of the firm. Naturally, doing better is really good, but on average, this is what businesses will achieve.
That is, business will sell a product at a price above marginal cost of labour in order to make a profit despite all the other costs, and will set the price to make sufficient profit in order to properly compensate stockholders. It's little different from having to pay interest on your debts, but in this case it's generating sufficient return for your stockholders.
Is it fair that these stockholders receive such a (usually) higher return? Yes, because they engage in a riskier venture than simple debt-holding.
I don't know what "equitable" means here. But a sophisticated Marxist response to the argument that wages are simply set by demand and supply in the labour market, I imagine, is that the market is not a 'neutral' and inhuman thing. The market partly consists of employers as buyers who have considerable capacity to set prices (i.e. wages), and very often it's the case that workers are simply price takers (in fact, I recall reading something by an economist that says workers are never price setters except it very rare cases). This leads to the possibility of exploitation, especially where employers collude with the authorities to depress wages or to deliberately keep working conditions sub-par, such as by preventing collective bargaining.
Perhaps buyers have a considerable capacity to set prices, but that's still not an issue. If I'm selling oranges, maybe I'm at a very disadvantaged position and can't set any prices. Their real worth is $1 per orange. A buyer may come by and offer me 50 cents an orange, and I'd be inclined to accept.
But if the oranges were truly worth $1 each, then someone else could then come in and offer me 75 cents per orange instead, and take all of the extra profit for themselves. And why wouldn't they? Why would they let 50 cents of profit go to someone else, when they could get 25 cents of profit for themselves.
The same works with wages and the market. Unless you posit a monopoly or cartel situation, which is not legal due to anti-trust laws, the market will find a fair and equitable wage for each person, or at least close to. The market may be "inhuman", but I daresay it's more effective at determining fair wages than any human that may try.
Suit yourself. What else did anyone expect you'd say? That's why I never really bothered trying to convince anyone here - a little knowledge is a stubborn thing. I simply answer questions about theory posed by anyone who has an intellectual curiosity. It's a much better bet to take the fight to the larger stage and debate not the merits of Communism, but whatever social issues are at hand from a Marxist perspective.
