When JD Rockefeller was growing up, the average American rode a horse (if lucky), never traveled more than a few miles from home, few had even been on a train. Sailing ships were the main and dangerous form of sea transport. 95% of Americans worked brutal farm labor jobs. Homes were lit by candle and whale oil, and heated with firewood.

By the time Standard Oil was broken up, railroads were everywhere, steel ships ruled the sea, cars roamed the roads. Homes were lit by electricity. Energy consumption had skyrocketed because the costs (esp. the cost of oil) had plummeted. Labor saving devices increased productivity and the standard of living, and were made possible by cheaper steel as well as cheaper energy.

That's great, but I don't see why you credit that to those companies being monopolies. There's no reason to think these positive things wouldn't have occurred for consumers just the same if there was more healthy competition in the steel and petroleum market. That just happens to be the technological change that was sweeping the world at the time.

It reminds me of Microsoft receiving credit for computers becoming pervasive and useful in everyday life, as if they deserve special recognition, or thanks, for brutally clawing their way to the top of a very profitable industry and ruthlessly suppressing competition, even when it meant scuttling superior technology. Clearly someone else would have made an OS for home and small business computing if Microsoft didn't.

And the same thing happened in other countries without Standard Oil and US Steel monopolies.