Folsom is right. The “robber baron” myth is an attack on free markets.
https://mises.org/library/truth-about-robber-barons
Yes, Rockefeller ran his business in a highly efficient and disciplined manner, but he scorned innovation and was notorious for greed and dishonest tactics in driving competitors out of business. He aimed at monopoly control and profits and won them even though it required bribery, fraud, intimidation, and market manipulation.
Similarly, Carnegie recognized that he personally was not capable of sufficiently severe methods needed to bring his steel business to maximum profitability so he made the ruthless Henry Clay Frick a partner and gave him operational control. Frick delivered substantial financial gains for Carnegie -- but at the price of alienating many business colleagues and much of the workforce. Driven to desperation, workers went on strike and helped spur the nascent American labor movement.
In time, many of the robber barons relented of their business conduct. Carnegie fired Frick, settled the notorious Homestead strike, sold his business to the House of Morgan, and devoted most of his fortune to philanthropy. Rockefeller similarly donated large sums to charity and the arts and spent much of his later years trying to develop a better public image and pass on his wealth to his offspring.
We should not let our opposition to socialism and Leftism blind us to unpleasant facts that are part of their critique of free markets, capitalism, and free societies. The laws against public corruption, business dishonesty, and market manipulation that the robber barons provoked were widely opposed by many businessmen when they were enacted. Yet those measures have made American business stronger and continue to protect entrepreneurs, investors, and customers. We should recognize those benefits and the history that inspired them.