This was a mainstream position. It was accepted that companies had to do well by their employees and the larger society, or something would be done to them by governments or unions. This was accompanied by boasting about "the American way", and that boasting was backed by reality. Things we view as acceptable behavior today, such as huge increases in the price of medicines, were not even considered. Mergers to the point of creating monopolies were rarely attempted and usually rejected.
But by the 1980s, it was clear that the USSR's system just wasn't working out. Capitalism had won. That's when it started acting like a monopoly, able to set the rules. This started in a big way with the deregulation of the 1980s and 1990s. This was justified by faith in a "free market".
But businesses didn't want a free market with many competitors. That keeps prices down and doesn't allow enough control. What resulted was repeated mergers, until most industries were dominated by a very few number of companies. This was promoted as desirable.[1] The US now has three big banks, three big drug-store chains, and three big cellular phone companies. None of those industries used to be that centralized.
So we've ended up with not only capitalism as a monopoly, but monopoly capitalism.
[1] https://www.wsj.com/articles/peter-thiel-competition-is-for-...