Earlier quoted context omitted.
The working class has never had it better than they have it right now, except for a brief period of a few years in the mid 20th century. You wouldn't know it though, from all the complaining. Sure, society "should" keep improving, but in the meantime there's plenty of ways for someone to improve their situation, and none of those ways involve complaining about rich people.
Do you mean they get to enjoy the fruits of modern life, and hence shouldn’t complain? Again, that’s not a valid argument. Let’s use some data, for example wealth distribution (1) - the lower classes have stayed lower income, and the middle class is rapidly transferring wealth to the upper classes. How is this sustainable? (1) https://www.pewresearch.org/social-trends/2020/01/09/trends-...
So when people spend so much mental energy complaining about how things aren't "fair", okay, sure, but you could instead just improve your situation. There will always be poor people, but an individual will not always be poor. We are not yet anywhere close to a situation where the highest expected value of an individual's time is to complain (instigating revolt).