A liberal looks at success and asks when is enough enough. A conservative looks at taxes and asks when is enough enough.
Alas, the myth of the "robber barons" is hard to break. I'm from Pittsburgh, where "robber baron" Andrew Carnegie made his fortune. Did he become one of the wealthiest men in history? Yes. Was that a given that he'd be one when he poured every last dollar he had (plus borrowing a ton) to invent the mass production of steel? No. But to do that, Carnegie had to have money to pursue his dream in the first place.
Carnegie didn't just create some jobs at his steel plants by investing his own capital, he created countless jobs around the world. He created whole industries. And he rightly became rich. And he donated almost all his fortune to others, enriching millions with (more than cash) libraries, culture and inspired more entrepreneurship.
The Bernie Sanders and Barack Obamas of the world would smother such dynamism in its crib. Socialists will never get it.