>I'm just responding that paying auto workers more would not result in a net benefit to the middle class. If as the parent's scenario implies there is nowhere else for manufacturers to find labor (which implies no outsourcing), then for every increase in automobile prices that's brought about by increases in auto workers' wages, that means less resources available for car buyers to spend on other things.
There is another party to the transaction, the owners of capital. Generally speaking, pro-union people argue that capital is in too strong of a negotiating position, and the workers need to unionize to negotiate against the owners of capital. If capital takes less profit, in theory, you can have lower prices and higher wages.
Yes, in the real world, it's messier than that. But, in all real-world business deals, yes, there is surplus value, but who gets that surplus value?
But the bit you are missing here, I think, is that the owners of the capital are a third party, and the more profit they take, the less surplus value is left for consumers or workers. (I'm not saying that eliminating profit would be a good thing, or even that minimizing profit is a good goal. I'm just saying, there are three parties to that negotiation. Three parties negotiating over that surplus value.)
you said:
>Unions in the American style cannot make the pie bigger, they can only divide it differently.
Which is exactly the point. Joining a union is very much the equivalent of hiring a lawyer (or other professional negotiator) to negotiate a business deal for me.
So yes, there is a conflict of interest. but there is /always/ a conflict of interest when trying to decide who gets the surplus value.