Post WW2, we had gradually managed to build a less violent society, and at some point, some CEOs decided: "You know, the Ludlow massacre and the Bisbee deportation were not that bad". And now, we get the pushback, where some employees think that murdering a CEO in the middle of Manhattan is fair game.
Rules didn't disappear. But people are more willing to go to conflict about them.
I don't think this is an accurate assessment. More of the violence was swept under the rug, but it was still there.
Post WW2 the US did well because a lot of old incumbent industries were disrupted by the war and swift technological advancements in many areas that opened up a lot of opportunities for scrappy startups. Also, the baby boom meant the workforce was skewed young and entitlements were not a major factor in the economy. Finally, the US had a federal government that was willing to tax the rich and not yet fully infiltrated by moneyed interests as well as an independent news media. Well, more independent than today's news media at least.
The primary problem with capitalism is that once you accumulate enough money it is easy to create a feedback loop where that money creates more money with little to no input on your part. This causes money to accumulate at the top where it has nothing to do but make more money. The primary advantage of capitalistic economies is that the power is pushed down to the edges closer to where the information is, but when allowed to run unchecked that advantage is lost as the power accumulates at the top, just like a command economy. This is why it is so important to tax the rich and to avoid creating billionaires, they can't efficient spend the money they have for the same reason communism doesn't scale well: the information bottleneck.