There are extremely good arguments for why the act of becoming and remaining a billionaire is immoral and bad alone, without any need for you to have directly wronged someone else.
PG just completely misunderstands and hand-waves over this basic concept and makes the excuse that "hey we worked really hard and made an amazing product that people loved, we aren't harming anyone."
For one thing, founders and employees don't share equally in the high growth rate of the company even though at most a founder is working let's say 2x longer hours than a salaried employee. You can do nothing wrong but you're still taking more of your fair share by the basic structure of how the business is setup.
I think anyone who is running a successful company and doesn't have a path to converting to an employee-owned enterprise is immoral, especially if you have managed to capture $1 billion just for yourself while your median employee is just making market rate salaries, or maybe they happened to gamble on your stock options and have a modest nest egg about 1/100th-1/50th the size of your wealth as a founder.
So yeah, Jeff Bezos made $260 billion dollars, but an alternative that could have happened was "Jeff Bezos makes $50 million and every Amazon employee gets a much more fair share of the happy customers' money."
More importantly, if you have $1 billion in net worth, that means that you can choose to do anything with your life on a daily basis.
When I'm over here working my job in my cushy upper middle class life, it's still an objective truth that I need to be selfish in order to secure the future of my family. Nothing is guaranteed and we need to fend for ourselves. I can't stop working or the home finances collapse within months or a short number of years if I'm very lucky and have something significant saved up or my house paid off. I legitimately don't have the time or money to help many other people outside of my nuclear and extended family.
But when you have a billion dollars (and some people have hundreds of those and one person even has a thousand of those), that means you have no limit to what you spend your time on. You can do anything, and deciding not to work on capitalist endeavors anymore has zero chance of turning you destitute.
In other words, when you are a billionaire, what you choose to spend your time on says a lot about the content of your character compared to someone who is not that wealthy.
Paul Graham is out here giving speeches to rich kids at Oxford Union, but he could be spending his morning in the local soup kitchen or building homes with Habitat for Humanity. He could be mentoring people who are struggling to escape housing insecurity, or he could be working with advocacy groups to expand healthcare access and end childhood hunger.
He doesn't have to go to work every day like I do. But he is one of the people who has dedicated his life to capitalism, even after successfully taking care of his family for many lifetimes, and that says a lot about him.