Has there ever been a union that pushed for lower compensation for it's members? A union advocating/negotiating for as much as it can for its members is exploiting its position in the same way.
No, trying to get a better compensation is not per se the issue. In a hypothetical company where the management takes home all the profits and the workers make minimum wage, moving to a more fair distribution of the profits involves less money for the management and more money for the workers.