For a lot of people (myself included) it is not mainly about the ethics of individual billionaires, its about the ethics of the existence of billionaires to begin with.
One of my good friends is a highly-paid engineer at a tech company, and he told me, "Businesses want to keep people poor, so they have cheap labor." Which is about as sensible as saying consumers want businesses to be poor, so we get cheaper products. This is actually a pervasive myth believed by many intelligent people.
Of course businesses want to pay as little as they can for labor, the same way literally anyone paying for anything wants to pay as little as possible. But other concerns obviously come into play as well, e.g. the quality of the people you hire, the affluence of the customers you can sell to, your top-level revenue numbers, etc. This should have been obvious to my friend, who works at a tech company that's happy to pay him and others $200k+.
The reality is that businesses actually prefer wealthy societies with wealthy customers who can buy more things. It's a chronic problem that poor communities are under-served by businesses, because poverty makes it harder to profit.
And yet the myth that businesses want people to be poor persists.
As does the myth that you can only make large sums of money through cheating, scamming, lying, stealing, etc.
This is wrong-headed but pervasive thinking. In reality, rich people are just people. Politicians are just people. Celebrities are just people. All people are corrupt to some degree, and some people are corrupt to a large degree.
It's easy for you to imagine a very wealthy person slipping into amoral hedonism, but I contend that their wealth has little to do with it. I once visited a rural Siberian village where a significant contingent of the older men wandered around town drunk. It was so commonplace that 10-year-olds in the community could tell you which of the men were angry drunks, and which ones could be led by the hand back to their homes. Those men lived on food rations from the government, and the first thing they would do when they got their ration of bread was to take it to the local convenience store and trade the bread for vodka. There are probably lots of reasons why someone would wallow in drunkenness for months at a time, but one reason is that they're just following whatever desires they have at any moment in time. Amoral hedonism isn't strictly a rich man's game.