The average operating margin for companies on the S&P 500, the "best of the best" of US corporations, is 9.35% - and that's a figure that is inflated by all of the pharma companies that have crazy 20% margins and sell into a dysfunctional drug market in the US and don't have to compete with generic drugs. Remove them and the operating margin is even lower.
There's no pot of gold in most cases. But I still think there's a good case for unionization.